Being gay doesn't have anything to do with motorcycles... maybe the person just wants to ride with like minded individuals... something else to relate to other than the bikes.
What does being a Christian have to do with riding motorcycles?.. Nothing... yet there are many Christian MC clubs and nobody seems to query them on why the emphasis on Christian... not to mention brand specific clubs, or women MCs or ...well y'all get the idea...probably the same situation with this person, only it's about being gay. People tend to want to hang with folks they can identify with.
and no I don't know any gay riders... at least not that I know of.