Hi Battis!
We rabbit owners know that there really are two different kinds of bites, both of which you’ve experienced. There is the nip, and the bite and I believe in that order, too. The NIP is pretty much stating “I don’t like that, please stop”. For example I helped my vet hold Cinder down while she was being examined and she was not hesitant to tell me she didn’t like it at all. It can also be trying to get your attention without broken skin. The BITE is a definite statement of “STOP!”, in my opinion. Where exactly were you petting him? I have read that rabbits don’t like being petted on the back or stomach (being prey creatures I believe), but Cinder doesn’t seem to mind. I think Cinder got quite a few good scars on me when I was trying to learn about rabbit behaviors the hard way. It’s not that she will bite every time, but I would go back and let us know if anything changed suddenly (hand placement, etc) to trigger this bite. It seems weird that he just up and bites, but it’s happened to me. Cinder has lunged at me for no apparent reason when I first got her! Hope this helps in any way.
Andrew