It is not a fair assessment. As straight males in this thread have stated, they like girl music. Unless they are closeted or the exception; I consider it unfair to base sexuality on music.
Males will get called gay for doing anything not in favor of male dominance. I've never heard a girl be called gay for listening to male artists. It isn't that is gay to listen to female artists, but it is feminine to contribute to female artists because it gives preference over men. Or power. A double standard started by men, much like majority of double standards.
Though I will say, I have used music to help in figure out a guys sexuality. I have yet to be wrong. Though what happens when a gay male doesn't listen to girly music? I could go on but then I'd reach the point of irrelevancy