Basically i was talking about grindr with my mates and my friend asked what it was so i told him it was a gay dating app the said he's not gay he doesn't think in quite a defensive way
I think the best thing for you to do is ask him. The only thing we can do is make assumptions. And that will lead you nowhere. If he is your friend, then ask him what he meant. Did he know that you were gay? Or maybe he made an assumption that you thought he was gay, and he defensively said he wasn't.
Again, I am making assumptions because I wasn't there. So the best thing you can do is ask him.