Yeah, I'm not so sure that 'someone' did that to your car. It's not that easy to play around with timing belts undetected...and you'd want to have a pretty good reason to go to the bother.
More likely that the mechanics who worked on your car a few weeks back fucked something up, or forgot to do something, or just plain failed to do something correctly and they're maybe covering tracks by saying 'someone else' did 'something' to your 'timing belt'. S'been done a million times before by tradespeople who don't really give a rat's ass.
But then maybe I'm just cynical and someone really did play funny buggers with your car.