this might ruffle some feathers, but...
Trenders absolutely do exist; some have openly admitted to claiming the "trans" label in order to fit in with a group or because they like the "aesthetic". There have been people already who attempted to medically transition, only to experience actual dysphoria as a result because they weren't trans in the first place. It does happen, and refusing to acknowledge this does the community no favors. Same with claiming that you don't need dysphoria to be trans, when dysphoria (the feeling of disconnect between your gender identity and your assigned sex) is the actual definition of the word. A lot of people are misinformed about what "having dysphoria" means, and wrongly equate it with "crippling 24/7 depression". But while that is the case for some people, no one is claiming that that's what it is for everyone. But if there is no disconnect, then you aren't actually identifying with a different sex from your assigned, thus you don't fit the definition of being trans. Everyone talks about "gatekeeping" like the worst thing in the world, but in order to actually protect trans people and help them get the medical care they need, it is very important to draw the line somewhere, and I think actually experiencing the symptoms of the condition you claim to have is a pretty fair place to draw it. Dysphoria might present itself differently for different people, but it is a part of the trans experience. If you didn't have it, then you wouldn't be uncomfortable being seen as your assigned sex in the first place. And if you aren't uncomfortable with that, then you aren't trans; it's OK to be gender nonconforming or to have issues with society's dependence on gender roles as a cis person. I get the desire to be inclusive and give people the benefit of the doubt, but no, not everyone who claims to be trans is trans. Trenders, fetishists, misinformed people, and even those just trying to make the group look bad ALL exist, and they are all at risk of undermining the trans community's fight for understanding, acceptance, and access to treatment.

As for the kind of people mentioned in the OP, I don't know them, so I can't say what they do or don't actually feel. Some people take a lot of time to allow themselves to begin transitioning, even after accepting their identities. It can be a confusing time, still living in the assigned gender role because it's convenient or familiar, but not agreeing with what that means in terms of how you will be perceived. Most will eventually move past that stage, assuming they really are trans. But there's also a chance they might not be, and just like the attention or sense of camaraderie they get for it, or maybe they just think they must be because of the things they like, without realizing that those things don't actually define a person's gender identity. It is very hard for someone who isn't trans to understand what identifying with a different sex from their assigned actually feels like. They may think they have an idea of what it is, which can lead to a mistaken ID. That's why it's so important to educate people on the difference between "gender identity", "gender roles", and "assigned sex".
I don't advocate calling people trenders just because they don't seem to have transitioned yet; you never know what their plans or reasons are. I try not to make too many assumptions and respect people's pronouns regardless of my opinions or suspicions. But some people need a reality check. If you've made no effort to begin transition, regardless of the reason, it should come as no surprise that people do not take you at your word when you claim to be the opposite sex from your presentation. It's not wrong for people to guess your gender based on the cues that you present to them. It may be rude of them to refuse to acknowledge it after you've corrected them, but it should come as no surprise if they have trouble when you make no effort to be seen as your gender.
Gender identity is not a social construct; it is inherent. You can't simply change it on a whim. Being trans is not a choice, a style, or a political statement. It is a medical condition and should be respected as such.

@SirLionelNigelConrad: That's the problem with this growing push for "de-medicalization", claiming you don't need dysphoria, etc.

I can't imagine why people who are trans would want to treat it like a choice after so many decades of fighting to get people to understand that it is not one. Yet I see more and more screaming about how gender identity shouldn't be treated like an inherent, biological thing? It makes no sense, and it just fuels those who seek to label it a fad or a mental illness, despite the science backing up the understanding of gender as a built-in part of how we are made. Those things give trans people a legitimate medical leg to stand on, which is important for receiving access to treatment, and show that there is more to what they've been saying than some "political agenda" or whatever it is so many people are trying to make it out to be these days.
Unsurprisingly, when you push the claim that there is no medical or biological reason to be trans, you end up with the current situation: losing access to protections, rights, healthcare, and social support. If it's not something inherent to a person, then it must be chosen, nothing more than a social move or a change of clothes. There is no need to take it seriously, and anyone who wants to can decide to be trans for whatever reason they please. You open the door for people who claim this "identity" for political reasons, sexual fetishes, and fashion statements. You confuse and muddy the definition of the word "trans" so that now anything remotely different from the most stereotypical ideas of "male" and "female" is "trans". You end up with people attempting to transition when they didn't need to, and regretting it. Then they go on to tell other people--trans people--that it's all made up and that we shouldn't encourage or allow it. You reinforce the idea that it's "dangerous" to let children explore gender roles and presentation, because doing so will make them think they are trans. Kids who actually are trans are not taken seriously because no one knows what the word even means any more.
There needs to be a clear definition defined by the medical facts and symptoms, just like with any other condition. "Trenders" might always exist, but we shouldn't be validating them even after they openly admit to using "trans" as an aesthetic or a statement. Nobody validates the edgy teenagers who self-diagnose with mental conditions and personality disorders. Nobody should be validating people who use "trans" as a synonym for "slightly gender nonconforming".
This is exactly WHY we have people claiming the trans label in order to get away with shitty things. They are piggybacking on the fight for rights and recognition, and no one can question them because "anyone who says they're trans is trans, even if they don't experience any of the symptoms, because gender isn't biological". Therefore, they make people believe that what they're doing is exactly what "being trans" is all about.
Saying you identify as a woman to get free access to women's spaces, without even presenting or passing as a woman, is a common joke now. Because that's how people view "trans", and this ongoing narrative that you don't need to meet any criteria whatsoever to be trans is exactly why. That narrative is transphobic. Treating it like a decision made for purely social reasons is transphobic. Saying that you need to actually be trans to be trans, is not.

It would be incorrect to say that trans people can't be criminals, predators, or assholes. Of course they can. They're just people. And I disagree with all the people I see claiming that XYZ person isn't trans solely because that person did something they disagree with. But sometimes, these people make it apparent that they're just claiming a label in order to get away with things, to elicit sympathy, or out of confusion over what that label really means. I don't presume to know if people like Jessica Yaniv are really trans, and it honestly doesn't matter to me if they are or not. My biggest concern is that what they do continues to feed the public view of trans people as deviants and predators. And that the ongoing push to make no distinction between people who adopt the label for the wrong reasons and people who genuinely experience it will continue to feed that perception.

@SirLionelNigelConrad: This brings up a very relevant issue.
While I certainly don't think any parents should rush to put their kids on blockers at the first suspicion they may be trans, I'm not a fan of that article. There's a lot of misinformation and fear mongering going around regarding HRT and puberty blockers, including mistakenly equating the two. Delayed or absent puberty is indeed something that needs to be looked into and treated, as it may not happen on its own, which can have a lot of health consequences. But a child on blockers will still eventually be taken off the blockers and go through puberty; which one will depend on their gender identity. That's basically the point: to delay permanent, potentially avoidable changes until the child is old enough to both mentally and physically handle transition, while also allowing them more time to come to understand their feelings about gender. I will always err on the side of caution when it comes to encouraging any kind of treatment that can have notable effects on the body or mind, especially those which may be long-term. To the best of my knowledge, though, blockers and HRT (at the appropriate ages and with proper medical supervision) are both safe and a much better answer than allowing a trans person of any age to suffer dysphoria. The permanent changes that can result from going through the "wrong" puberty can have a devastating effect on a young person and make transition more difficult--physically, socially, emotionally, and financially. It's a good reason for blockers to be considered, provided there is enough reason and evidence to believe that the child may actually be trans.
This is a pretty good point to bring up, as it balances on the edge of that question, "Where do we draw the line?" It can be a hard one to answer, especially for a parent whose child's health may be at risk if decisions are rushed into in either direction. But in all my reading about the subject so far, the conclusion I've drawn is that blockers are not a danger--and certainly not a significant one--when you remember, despite what that particular article implies, that they are not going to be taking them forever. I would be surprised if there were no health effects at all, of course, but in this case I do think the risks are minimal and greatly outweighed by the benefits. I think it would be better for a child to be on blockers for a time and end up "desisting" than to be refused any treatment and go through the wrong puberty.
Do I think we should believe anyone and everyone who claims to be trans without looking for any sign of evidence? No. That's dangerous for everyone involved and for the trans community as a whole. However, I do think everyone who makes this claim should at least be given the benefit of the doubt, up to a reasonable point. Trans people differ greatly from one to the next, just like cis people. It's equally dangerous to encourage people to disbelieve anyone claiming to be trans on principle. We should always give people the benefit of the doubt, and likewise we should always consider the surrounding evidence of any claims. Things like not transitioning for any reason (there are many reasons, such as family obligation, social pressure, financial strain, etc) are not evidence to invalidate someone's identity as trans. But when someone outright states that they do not fit the very definition of being trans, or that no one should have to in order to adopt the label, that is where I do draw the line.
It's already tough enough for trans people to be believed. I can see why there would be a push to say "believe everyone". And I think, to an extent, that's fine. But I've seen a lot of people pushing much further than that, and essentially a growing culture of seeing "trans" where it isn't. I've seen people who were not trans but gender nonconforming in some way being poked and prodded in an attempt to persuade them that they are in some way trans. People need to chill, and words need definitions.