it seems unlikely that the average of US teens is overreporting

On the contrary! I do think many of these teens are just lost and try to tag themselves to a group just so they feel they belong somewhere. It might be caused by a plague of unstability in teens' homes as normally functioning family comes in a premium these days. As much as some people would have desired most of them are simply cishets, like it or not. Claiming that 1 per every 4 people in our societ is LGBT is strongly exaggerated. It also depends on where do you live so your claims might be biased. In my place there's no way even 1 in 10 people is some kind of gay.

You can check my profile, I claim it as some kind of LGBT myself. Also I do think that respect and representation are different things.