I know this through observation, and not because we used to sneak friends in through them at some time in a misspent youth.
In you theater, is there perhaps an alarm on a timer so that before the movie and while the movie is playing, the door cannot be opened without an alarm sounding? Then when the movie is over, the alarm is off?
I guess this will all come to light.
If the theater operated under normal industry wide standards regarding the exit door, then they probably can’t be found at fault on these grounds.
But if it is found that it did not implement industry wide standards regarding exit doors or that the exit door mechanism was not maintained, lawyers will crucify them.