1993 Toyota Camry Drove with no oil cap. Whats the damage

Engine Mechanical problem
1993 Toyota Camry

1993 toyota camry, new engine three yrs ago. I recently had an oil change but the car was returned with no oil cap. I drove for a week (aprox 150 miles) and noticed that the car was stalling whenever I let it idle too long. Finally checked under the hood and replaced the cap, (the facility that changed the oil admitted fault) but ever since then the car has been running rough. There is an abnormally high pitched whine and it now has alot of trouble getting up an incline. I had a mechanic look at it and was told that the whine is coming from the timing belt area, and that the whole kit (including the water pump) needs replacing. He mentioned that there is a hydraulic tensioner under one of the pulleys on the timing kit that uses oil pressure to keep the belt taut. Could the facility that left off the oil cap be responsible for the damage? What other damage may they have caused?