1997 Ford Escort timing belt

I took my car to the shop because while driving sometimes it would act like it wanted to die and lose power. This would last for a few seconds then it would be fine. The engine light would flash too.
I drove it to the shop and it acted fine. Later the mechanic called and said my engine was shot. They had started it and pulled it in the garage and said they shut it off and checked for vaccum leaks and when they tried to restart it then it started knocking and the they said the timing belt had jumped and bent the valves. Would't the car have been running when they checked for vacuum leaks and shouldn't they have checked the timing belt at that time too? I just keep thinking there is something strange about all of this. Please help