Sounds to me like he's struggling with his sexuality. Homophobia can often be used as a cover-up for people feeling insecure about possibly being gay/bisexual themselves. The fact that he experimented when he was younger shows that he was confused at some point, or at least curious. Maybe he realized he wasn't straight back then and is trying to shove it away. Being unwilling to meet your gay stepbrother may also be part of that...he may just want to avoid the whole subject at times. But the fact that he went to a gay bar makes me think he still feels the need to be himself, or try to be ok with who he may be.

That's just one theory to think about. It may not be the case but I've seen similar things happen with many people, so it is possible.
However it's also possible that he went to a drag show viewing it as some kind of joke...who knows.

I think you should just try to talk to him about it. It might not get you anywhere, especially if I was right about him maybe being gay, but he just might talk if he feels its safe to do so. Who knows.