From what I understand, if the copilot was in his seat it would have been a simple, almost non-event. pull back would sum the inputs to level (one full down the other full up), computer shouting at you for dual inputs. Then press button, take control , work out what went wrong
As it was the co-pilot wasn't there to take control, he was out of the cockpit and had to crawl back in on the ceiling due to negative G and by the time he managed to get near his controls the airbus had decided by itself that this was a "bad thing" and brought nose up / power down meaning some kind of return to normality.
there seemed to be a determined attempt to remove slices of the swiss cheese here though:
- so pilot alone in cockpit for extended period
- alone pilot bored
- alone pilot decides to relieve boredom by getting out camera and taking pictures
- pilot possibly interrupted taking pictures by the purser and puts camera down in inappropriate position
you have to question all of those
That is stupid and maybe unprofessional but a lesson that can be learned from. if indeed he then tried to cover all this up, that's a crime in my eyes.