Twitter comprises innumerable subcultures. Whatever in the world you may be interested in, there are probably people who connect on Twitter about it (or Reddit or wherever), and they often call that sub-culture "X Twitter." If you're proud of your eating disorder, there is literally "edtwt" That's "eating disorder Twitter." Weird example, I know, but just to say, just about anything you can think of, there's a Twitter for it.
Of course there's a gay subculture on Twitter, talking witty about gay topics. Hence, gay Twitter. It's no more insulting to refer to it than it is to say "gay bar." It's just a fact.