I assume that the G's associated with this manuever are known from the DFDR as well (that would have been more interesting to me had they released them). Although, I suspect that the G's from the DFDR only reflect a specific aircraft loacation and would have to be extrapolated to the aft cabin passengers.
I'm trying to get a feel for this and I suspect that it might be like riding a roller coaster where some dude stands up to wave his arms and is ejected, only in this case the passenger ends up hitting the ceiling panels. The passengers still buckled up would feel it in the pit of their stomach.
Seems like many causative possibilities are still open including commanded (either via cockpit or computer) as well as uncommanded (something breaks or a servo sticks)