Your car has the individual coils over the spark plugs, it would be possible to have pinched a wire harness if he removed one of the hold down bolts for the coils. Heck, I almost did that very thing just yesterday. Being a technician myself I hate being "ever sinced" by a customer but you may have a connection there. I doubt that there is anything he could do with the belt install that would effect just one cylinder but it is neccesary to remove the coil/spark plug covers to do the belt. Why he would have call to mess with the plugs and coils I do not know but it could have been something inadvertant that he was totally unaware of. Could've been a faulty coil or connection to start with and he disturbed it just enough to cause this problem. I would pull the cover and take a careful look at the coil that is supposed to be offline without moving or disturbing anything. If you do not see anything then I would give him a call and take it back.

Mark