Confused about the concept of sexuality

First ever Reddit post, so idk correct me in the comments if I'm doing something wrong.

So my moms friend and her son (M18) comes over, I (M20) am not really friends with him but we were hanging out, from what I know he presents as that type of straight guy who's just obsessed with girls and is trying to hit on them, I on the other hand am gay (not openly), I usually am not really a extrovert kind of guy who can socialise easily with someone new but with him I got along quite well, most of the conversations were just he fussing over some girls he tryna hit on and what should he say etc, It seemed like he was in the same teen phase I was in when I was around 16-17 where I would just be freaking horny most of the time, he ends up opening and discussing his secret folder full of girls and porn.

As some sort of tension builds up (idk if its just me or him too), I finally decide to make a move anyway, something like "damn bro I'm getting hard, wbu?" (Trying to get his attention on my bulge), he says "ig, damn you are hard" (looking at my bulge), I say "go ahead, touch it". To my surprise he actually does it without hesitation and I touch his, we move to the bed kissing, making out and even oral. We started giving eachother handjob but we had to stop because there wasn't much privacy.

I was really not expecting him doing any of this with me. Later I ask him if he had done this with any other guy and he said no just with girls and that he was actually imagining a girl while doing all this.

What I'm wondering if is he straight? Is he just closeted maybe? Or is it something like even if you identify and behave to a certain label you still can act differently?

I had another experience a few years ago that was almost the same as this one, in that one, after we're done the guy just dressed up and behaved like nothing happened and we continued the sleepover, it was a lot hotter but that's a story for another time!