This is a strange one. My year old DS now bfed before bed and first thing in morning. He always asks to be fed. But for the past month after EVERY feed he will gently (hard to believe it can be gentle but it is) place his front teeth (he has eight!) around my nipple and pull quickly off the breast so that it kind of hurts but can't quite be described as a bite.
I am puzzled about what is going on - it seems to say 'I've finished' but why would he do this?
I wonder if it's simply a habit he's got into which initially got a reaction when I 'yelped' so he has continued?
Could he be telling me he doesn't want to bfeed any more? I think this is unlikely but you never know...
TBH I think your first guess is more likely to be right. If he didn't want to BF I'm sure he would neither ask nor do it! Kids who go on a nursing strike or self-wean (and they're sometimes confused) will refuse to take the breast point blank. Maybe he finds it fun? Is it bothering you? If so you can tell him no, or try to quickly whip your top down when you see him going for the bite