that he is good.
Everyone needs that. The question is by how much.
That self-confidence you said he lacks should come from within himself. Being a medical school student, how much external reassurance does he still need?
The key is being willing to be responsible for himself, and to have no need for external buttress.
If he didn't get the tutoring job, does it mean his lack of self-confidence is warranted?
Congratulations!
(His lack of self-confidence may stem from that he needs to prove to you, again and again, by providing evidence that he is good. Take it as a price to pay for him becoming an MD. There should always be a better way to do something.)