After all that torment/teasing he just exploded. The first squirt went over his head and several more landed on his face. No telling how long his master kept him chaste before this session, but he was loaded. Plus, he is young and fit. I think I'd have kept him there and milked him out until he had nothing left to give. Followed by a good canning to make him even more compliant and anxious to please, then take him to bed.
You are absolutely correct to always pair punishment and sex. Eventually pain and pleasure get mixed up in his head and associated with you. Then you truly own him.