Are you really that surprised?
Everyone sees everyone else filtered through the lens of themselves. By the time I found out girls thought I was hot AF in high school, decades had passed and it was too late to do anything about it. It's not that I wasn't told as such then; it's that I was so wrapped up in my own self that I couldn't accept it.
I'm still that way, but at least now I sometimes, on occasion, am aware of it.
There's no universal sexuality, but this, at least, IS universal. We all do this; sometimes we can be made aware of it.
I think it's slightly easier for those who are LGBTQ+ to recognize that not everyone has the same sexuality, because the difference between what everyone expects of them vs what they are is just hammered into their heads every day of their lives.
For cis, straight, "normal" people, it's too easy to think, "That's just wrong" and go about their lives. It's only the point where someone we care about comes out that we have to face our own bigotry. That's happened to me twice.