What kind of school do you go to? People thought I was gay in rural New Zealand because I had no interest in rugby, was softly spoken, and no good at sports, that was all it took. I had never even heard of the word "transgendered" back then though.
I like to think also that "gay" has only one syllable, like "->-bleeped-<-" (another word used to describe me) and that the people who liked to use it were of limited intelligence and probably wouldn't have been able handle "difficult" words like "transgender" to start with!
Seriously though, despite the best efforts of bears, behaviour that is perceived as effeminate in males is usually connected to the idea of being gay for a lot of people.