If his carving tools were part of his job requirements, then he should be okay. But since they are not part of his job requirements to have them (based off the limited information provided), he's S.O.L.
He should be keeping both of his work tools and recreational tools in separate bags. As you have mentioned that he kept both his work tools and carving tools in the same bag, it's possible that his job required tools may have damaged the case. This could have caused one of his carving tools to come out and result in the injury. If that is not the case, he was negligent in that he didn't make sure the case was properly secured and/or in good shape, and if the bag would be able to withstand something like that.
In the end, he should never have mixed his work required tools with his recreational carving tools in the same bag.
As for Workman's Comp, he will have to talk to a lawyer to get the information he wants. Tell him to call a lawyer if he wishes to take the matter to court, however it's very likely that they will lose the case. Again, this is only based off the limited information you have provided.