This easily could have happened if the cell was not properly de-energized prior to entry. There are tons of examples of people improperly locking out a robot cell and the robot moving unexpectedly while repairing it. If indeed this person was a contractor it is very conceivable that a lockout violation occurred and resulted in death. A lot of the robots in a car plant are quite large. Take into consideration the one in the photo below (spoilered for size). Imagine being struck by one of these?