Did he short all the locks at the same time? On the particular lifts I learned on there was a relay in between the locks to not let the lift run by a short across both locks.
But this is a good lesson to new mechanics. Check the level of the lift on the entry level, go to that floor and check the doors and close them if necessary. Then check your locks, but never ever short both landing locks and car door together without assistance. 1 landing lock or car door by its self only. Even then ny closing the doors(or by checking and making sure the doors are closed on entry to the building), you can then place the lift on maintenance control and drive the lift to where you can get on top. Either way you DONT short all the lock at the same time without assistance.