Sorry, I think most of these responses are way off base.
I think it was obviously the contractor's fault. If a mechanic fixes your brakes and forgets to torque your lug nuts and the wheels fall off, it's obviously his fault, even through you didn't hire him to torque your lug nuts. Is it your responsibility to take the wheels off yourself before the mechanic works on your car, since they're just in the way of the brakes? Of course it isn't. If you need to move something to do a job, it becomes part of the job, and replacing what you move then also becomes part of the job. That's just common sense. Which is why when you look at the job description your mechanic gives you, it will usually specifically list "re-torque lug nuts to manufacturer specifications," or something similar at the end of the job.
The contractor didn't finish the job, period. Now, I doubt he charged you for the time it would have taken to plug the fridge back in, so it's not like it was fraud. But if a mechanic says, "OK, all done," and all the wheels are still off the car, the customer has every right to be upset. It should be an implicit part of the work that was requested and shouldn't have to be explicitly requested by the customer.
But you'd never get him to pay for it. You know who not to call or recommend to your friends next time around. Bummer!