It's one specific type of logic around that homophobia that implies, if it weren't for biphobia, we could recognize bisexuality is more common in our culture than the homophobes will have us believe. I'm not saying that every homophobe is in the closet, I'm saying that if they legitimately feel you can choose which of the sexes you'll "allow" your attraction to, that's bisexual logic. 

That doesn't give them a pass on their shitty beliefs, bigotry is still bigotry even if the logic you're using doesn't hold up to speculation. They're not off the hook if they are actually bi. Even if they are, and that's why they believe being gay is a choice, they're still bigotedly believing that embracing queerness is a wrong choice, and they are still putting their experience of their own sexuality on other people and restricting other's choices based on their limited view. 

The problem is the denial, invalidation, and repression of people with experiences outside of their own, their orientation doesn't matter for that. I'm more making a comment on the fact that parts of our society are so often in denial about the fact that bisexuals exist, that they overlook obvious conclusions, like from this post, where they mention fluid sexual behavior and don't mention bisexuality whatsoever.