I cannot for the life of me understand how anyone can possibly conclude that sexual attraction is a choice. Unless YOU personally feel attraction for both sexes. Do you? If so, then you are bi-sexual. Whether you acknowledge the fact or not.
I do not recall one time in my entire life where I made the deliberate choice not to feel attracted to a person of the same sex. That makes me a heterosexual. I have found many of my sex attractive, but have never felt any desire to take it further than pure appreciation for a beautiful human. Hell, I can't even control the attractions I feel for the opposite sex.