Sounds like he wasn't really into guys after trying it, he was curious so he tried it and that's ok. I don't think it makes the guy gay but he did do something gay once and it sounds like he had to get that off his chest. Or alternatively he was testing the waters to see if you were down for some gay shit.
I had a close friend when I was 20 that I spent a lot of time with, one time we were sitting in his car outside a party at his apartment and he awkwardly said something along the lines of "we could totally gay it out and not tell anyone" I told him I don't want to do that but it's ok we can still chill. I think he was pretty disappointed, like he shot his shot and I rejected him and it probably took a lot of courage for him to do that. I think about that every now and then. He was a twink type and at this point in my life I would have probably took him up on the offer but I don't really know if I'm just more secure now or if the Tren did this to me.