Thankie for advice! I'll give him a while then maybe try to hold him again (with washed hands of course) and just try to watch his movements very closely to figure out if its a yawn or a food bite. This last time with the thumb there wasn't any "nuzzling" before. He was resting his chin on my palm/thumb area then after a bit started to turn his head sideways and open his mouth so I just moved that hand away.
If it is a mistaking for food kind of bite, with more handling do you think that association will break over time?
Right now he is eating frozen thawed 'medium' mouse once every 5 days (going by the 'width of their girth' rule of thumb).