(Ex)Pop star Brian Ferry (left) looks on in this shot:
I have no doubt that it was on autopilot, and BBC reports say the autopilot disengaged. That's actually a design feature.
Boeing Autopilots don't argue with crew (and Airbus A300 auto pilots don't do it any longer, at least not in the aftermath of one of the CAL accidents in Japan that resulted in the crash of an A300 because of just such an argument). I.E. any substantial movement of the controls, either by accident or deliberately is likely to disengage the autopilot (which you are warned about by a Klaxon horn going off). (The Klaxon horn is the result of another accident, an Eastern Airlines Tri-star that flew into the Florida Everglades, in part because the autopilot had been accidentally disengaged, and no one realized it had happened).
Autopilot servos are invariable 'low power' to insure that they CAN be overridden by flight crew should the need arise.
While the maneuvers may have been violent from a passenger view point, obviously from an airframe view, they probably weren't all that dramatic. The most serious injury is one broken ankle.
I am compelled to point out that accelerations of -1G or +2G have in fact caused death and serious injuries on airlines (usually due to FA's or passengers sailing into the ceiling before being dumped back down on the cabin floor). The fact that the total injuries is only 4, and none serious suggests to me that relative to the aircraft limits, these weren't all that violent.
The other feature of those extreme accelerations is the cabin usually looks like a Cyclone has been through it. Everything that wasn't restrained (newspapers, magazines, blankets, pillows, shoes, pocket books, computers etc) enters uncontrolled flight and is randomly re-distributed throughout the cabin. It's a memorable experience.
As far as regaining control, if things aren't really hose up,, if you just stop the off the wall control inputs, the aircraft will generally sort itself out reasonably well. That's a certification requirement.
If you want to talk about violent maneuvers, take a good look at a near disaster with China Airlines in the late 1980's with a 747SP off the Coast of California. They changed the dihedral on the wing, and managed to pull 6 g's, probably a record for an aircraft in RPT (and well outside the airframe design limits)..
The other claim from the BBC is the engines cut out. I find that very unlikely, however in a dive, the autothrottles will reduce power to flight idle, which coupled with the aerodynamic noises, might well mask the reduced engine noise. Short of fuel exhaustion, mechanical failure, flight into a cloud of volcanic ash or absolutely awful weather, it is pretty hard to get the engines to actually cut out.
From the Daily Telegraph in the UK:
The attacker after he earned his "upgrade":
(Still on vacation!)