Straight, gay or lying?

According to this article, there are few if any, true male bisexual:

People who claim bisexuality, according to these critics, are usually homosexual, but are ambivalent about their homosexuality or simply closeted. "You're either gay, straight or lying," as some gay men have put it.

In the new study, a team of psychologists directly measured genital arousal patterns in response to images of men and women. The psychologists found that men who identified themselves as bisexual were in fact exclusively aroused by either one sex or the other, usually by other men.

I could see how, depending on the circumstances, a person who was primarily homosexual would try to feel desire toward women as well.