I don't see how saying, "I've done gay stuff" is any different than saying "I've had some same sex experiences". It sounds a little more down to earth really.
And I can totally see a gay person saying "I've done straight stuff". It just means you've been there but it's not your main identity.
Yup, just a down to earth, casual way of referring to what he's done in the past is exactly what I took from his posts, not "Ah-ha! He used the wrong words therefore he's obviously a liar!"