I don't think "people shrimp" is all that hard, was it still shelled? he may have accidently bit a rock or something while eating the shrimp. my fahaka pickes up peices of gravel thinking they are snails sometimes and I worry about the same thing. the best thing I think you can do is keep an eye on it and see how it goes. I don't see it being a problem because puffers teeth grow throughout their lives. after a few snail, mussels, crayfish it should be fine.
HTH