The initial error was not grave, the resultant handling of the aircraft leads to some very serious questions about the level of competency displayed.
Again, not a large aircraft pilot but I imagine a sudden rapid -2g descent in the middle of a bog standard cruise, is not regularly practiced in the sim. The Captains first action was to pull back on stick, seems natural enough to me, and then when that did nothing and autopilot would not disconnect I can only imagine the confusion.
Before jumping on the outrage bus at this one individual, perhaps if these drills are incorrect, (and I don't know) then learning can occur.
Still, sure all here would have dealt with it perfectly , would have had no loose articles on the flight deck etc etc. perhaps attitudes here are a generational thing.