I think he should get paid unless he skips out often, but you said he was good. Sometimes they have to work more than average too(like when they come back the next time because of the missed week). It’s just a way for him to average it out and know what he makes month to month.
He just agreed with you because he doesn’t want to lose the account but it could have justifiably gone his way on this one.
I’d would have let him keep it , reminding him perhaps, that he has the account because he puts in a little extra in when needed … and thank him for his good work.