I'm still leaning towards he didn't have the wheels snug against the hub when he switched wheels.... so the camber was off tilting the wheel towards the caliper. It does not sound like he has a caliper defect, the problem would be uniformed w/ both wheels (assuming his left and right wheels are the same).

I'd switch it one more time and just make sure the wheel is on there nice and tight.... hand tighten while the car is on jacks, make sure to wiggle wiggle to make sure the hub is snug..... take it down and tighten it down.....

alot of times when a car is jacked up and you tighten the lugs.... the top of the wheel is tilted in as the weight is unbalanced..... you tighten and the lugs feel tight but the hub remains un-uniformly flush.... just my .02 cents.