I think your right. I kinda get what the author is saying with the character but I also think the way it was stated makes it sound incorrect/off. She (the character in question) probably dose have gender issues and just writing it off as being "bi" is not the best explanation ... I can understand though since I'm bi and I have a masculine side that likes to pop up when I'm around women... even though I don't think of myself as gender queer or fluid I sometimes wonder about myself... I've been accused of speaking/acting in masculine ways around women some times. Its kind of a mote point for me since I'm with a guy rite now and I'm almost 90% feminine when I'm with a guy (its just how I react/am?) but still.
The way they define bisexual makes me cringe but the story is making a nice attempt and for that's good.