"Bet it was left tripped by engineering after their work..."
Pure rubbish. Do a bit of research and find out which systems are powered by the popped c/b. Then, do a bit more research and determine when these different systems are used in the course of operating the aircraft. You will clearly be able to determine that the c/b popped AFTER a certain point in time.....and this point in time was after the flight crew was operating the aircraft.
You wont be able to determine why it popped or exactly when it popped but it should be clear (and easy to determine) that it popped AFTER the aircraft was configured for flight.