Please do not jump up and shout at me. I AM NOT SAYING THIS COULD HAVE HAPPENED IN THIS CASE.
When my company first got their A320's we had similar incident. The cause was put down to the F/O sitting cross legged and his Knee pressing on to the side stick. If I remember correctly they thought either the pressure gradually increased untill the autopilot let go or that he moved and knocked the side stick hard over. Neither pilot could remember this happening but the FDR showed the side stick movement.
Again if I remember rightly the a/c went 60 deg one way then 60 the other as the other pilot grabbed his side stick to correct. Then a bit of dual stick input (it sums the inputs) untill things settled down. Luckily no one was hurt.
Anyway as a matter of interest. & be careful crossing your legs, especially with one ankle on the oposite knee in an Airbus.
