Agreed, had to be someone that knew of the car. Mention to anyone it was going to be out in a shop? It was either a serious case of dumb luck (in the thiefs case), or your car was the target.
When I had my bird, and took it to a shop once, it confirmed I won't leave it alone when possible. Bastards shoved the car onto their street in a crap neighborhood. Waited two hours for a tow truck (electrical issue they couldn't diagnose), and in that time watched a few different cars slow and case the car...including two guys who drove and stopped three times.
Just can't trust leaving anything unattended anywhere, for any give time. Granted this is not meant to offend KK since this was likely a one time incident.