To me it seems like these people (based on what you're saying) would probably be more accurately described as genderqueer/something else other than male or female, but are identifying with the ftm community, probably because either they have shared experiences, or they just really want to be part of a community and can't find one for their more specific identity. And while I can see why the latter would confuse the issue, I don't know what's the problem with the former. I mean, there are people who've physically/socially transitioned in a typical "ftm" way and yet they don't identify as male, even though they went from being perceived as female to being perceived as male. It seems reasonable for them to consider themselves "ftm" if they want to, because they share so many experiences with other people who consider themselves ftm.
I also think that a lot of people might just be going through a phase where they're still coming to terms with being trans. If you're uncertain and you realize there are a bunch of people who don't identify as strictly male or female, you think "oh thank goodness, I can just be that, and don't have to do all this transitioning stuff that seems terrifying and unfeasible." But if you actually are male, you'd probably find yourself gravitating towards terms like ftm, even if you haven't worked it all through yet.
If you're a kid and you have no support system then it's much easier to only go halfway, if you can live with it. I know when I was 13-14 I was all "I'm a boy, I'm going to get surgery and hormones, but I'm not transgender, oh no, because that is far too unlikely, I mean what are the odds?!" Which is kind of the opposite of what these people are doing, but all I'm saying is that being extremely illogical about it is something that happens.
