Sounds like a genuine misunderstanding to me, if he thought you were a semi-gaylord as well.
Say to the bloke that you don't have a gay bone in your body and you certainly don't want his gay bone in your body. That you think he's an OK guy and that you would like to be blokey mates. That if he's cool with that you would be all like made up and stuff. However he must understand that you will not tolerate any further attempts at hawt man-on-man action. That this is not a negotiable position.
He may just have been chatting you up in the first place and doesn't really want to be just mates. You are quite the eye-candy after all.
Alternatively you could pump his arse rotten and see if you like it. You never know until you try it. Anyway it's only gay if you take it up the arse, not if you give it. That's what the lads in prison told me.