I will suggest that a front hinged canopy opening in flight will change the airflow over the horizontal stab. My off-the-cuff visualization suggest the result will be pitch up. If the pilot flying overreacts and pushes nose down too much too fast, which might cause the canopy to open further, might add up to how an unbelted individual could get started exiting the aircraft.

I have been in the back of a cargo aircraft when the pilot put us into zero G. I started to float out the open door. A friend who was anchored grabbed me and pulled me back inside. I was intending, and equipped to leave the airplane, but that particular spot would have been inconvenient.

So it is possible that the change in aircraft flight characteristics and the pilot reaction, combined with the deceased being unharnessed, could have resulted in what we see.

Fly safe,

Wes
N78PS