Steve,
I think you are right on point. He subbed it out to someone else. Especially if you used him in the past. Looks to me like the concrete he was using setup to quick OR, he didn't have enough going at one time. She sagged quite a bit.

Time for a jackhammer, a wheel borrow, and a do-over on that one. IF he did have someone else do it, I'll bet he never even went out and looked at it! OR, if he did, and he was okay with it, I would NOT be calling him back again.