I've seen plenty of crew cramming bags in and then forcing the door to close. Sometimes even two crew members working together, each pushing the ends closed. They do seem quite robust and able to take a battering. Sounds like on this occasion it just had too much. But that's going to happen more and more due to BA's policies and their efforts to cram more seats into their planes.
To be honest they should change 'hand baggage only' to 'checked baggage only' and be done with it.