Here from Americans occaisionally such things. I think it's kinda unusual even for Americans though.

Like I've heard from some American friends of mine that they didn't know what a period was until after they had had their first. And that seems very strange to me because I knew girls had periods since elementary school at least.

I think some Americans have this strong taboo towards bodily functions. Not even sex just the basic mechanics of reproduction. Probably why you see these ideas spread so easily because if you don't understand the basic biological differences of sex then you'll end up believing that it's just how you dress or what not.