Yes, his repair meets standards I use all the time. Just finished a bathroom remodel using very similar techniques.
The price? Consider it another way ... if the job had EXCEEDED three days, he would have charged you the full price of the overage. You would not get a break, right? So you can't have 100% upside coverage but refuse to cover downside discounts. If the job was completed because he over-estimated the job it is NOT your fault, it is his.
When contracting you need to get an hourly rate as well as a day-rate. If he chooses to add 5 people to the job, you need to pre-approve the overage. Quick work lets him finish and move to the next job, thus, you both win.
I would take it upstairs to the Manager and insist on a reduction using my logic.
Oh, if you get a discount, send Neal and me some coupons for burgers and beers.