Although now I'm finding that a lot of people who think they're bisexual when they're not. I see this in a lot of autistic individuals, they think that just because you can tell the difference between an attractive individual and an unattractive individual that that is indicative of sexual attraction, also I've seen "my (opposite sex) partner says they don't have a gender, therefore that must make me bisexual".
Yeah, I think this is true. And also younger people (early teens) seem to be a little confused about it along similar lines. I also think where you have younger people especially who aren't sexually active, and they see very attractive movie starts, or explicit material in films, or porn, and it's arousing, that often does not really correspond to adult sexuality in a clear way. So you have a teen girl maybe watching porn that involves women and finding it arousing, but really it's because porn is designed to push certain buttons.
Finding a young movie star sexually attractive at some level is not the same as being potentially interested in a regular middle aged woman later in life, if that makes sense? In the same way that your average straight woman is often interested in your average straight man, even if he is not young and hot.
I really think this is part of the reason so any more young people tend to identify as bi-sexual but later it falls by the wayside.