@Karel_x:
This, from the New York Times (emphasis added):
No passengers were on the plane, which was connected to an external ground power source, according to people briefed on the incident.
This make the comments from ATC Watcher and mad_jock especially relevant.
What is the usual electric power configuration established by the crew when they leave the airplane? What are the airline's procedures for this? Did the flight / cleaning / maintenance crews adhere to the procedures?
My "common sense" take is that the cautious course would be to disable all galley power when people aren't on board.