Not sure how but I am convinced there was a catastrophic power lost into the copters rotor system. If it was one motor I believe it would have flipped over one or many times.
When you see the video in a slowed down speed you will noticed both motor that come into view are spinning in the opposite direction of what they should when powered. The aircraft in this state is auto-rotating, this is when the air comes up from below forcing the rotor system to automatically rotate in the favorable direction, on a fixed propeller this would be the opposite of what is needed to produce lift.
Because the camera never went dark, tells me some type of power was always present. If you caused a full shut off while in flight by crossing your sticks like when you start the copter up, then you could induce this type of drop, and maybe the flight logs would end, however it still does not explain why the gimbal changed its orientation.
This is a very interesting case, to me.
As of settling with power I would wipe that thought out, it deals with vortices and quick descents. This video does not support that especially when the camera goes lose then comes back facing a different direction, and seeming to work properly.
Something catastrophic happened, a hiccup of some sort to the rotor system/possibly IMU, and unlike the post before stating they thought it was pilot error I would favor not, but not rule it out,
I just can not see how a pilot error would cause the gimbal to respond the way it did, while having other issues in the craft at the same time.