So was it "Thousands" of feet, or just 600?
The maneuver as described could have been quite mild (descending about 30ft/s, if those figures are accurate), but with sufficient acceleration (at the pushover) to cause a very unpleasant upset to people and objects that were not restrained in the cabin.
Aside from that, I'm curious why it isn't mandatory to have your belt fastened at all times - I'm 6'3", and uncomfortable in most aeroplanes, but I still leave it on because I know these things can happen, and the belt doesn't bother me at all.