Unfortunately that just happens sometimes. Some vets just don't know how to pull teeth properly (yikes, eh?). Not all vets are good and very young vets usually don't get near my kiddos. I like experience. And also xrays are technically supposed to be taken when extracting baby teeth although nobody does it. I imagine that would avoid some of these types of problems. He'll be fine, I'm sure.
They really don't miss the teeth that they lose. He'll be in much less oral pain now.