Seems an odd anecdote to exist there without any citation at all. Assuming it's true, he was clearly doing it to make a point, and therefore maybe he picked a subject that would make the point (i.e. it had to be something that wasn't politically correct) but wouldn't tarnish his reputation - if he had stood there making racist remarks then people might consider him a racist, whereas a gay person making homophobic remarks he could, if called on it later, say "of course that's not a reason to judge me, I'm gay myself!".

(Alternatively, it's not too uncommon for people to be homophobic either because they don't understand their sexuality, or because they understand it but want to hide it from other people.)