It’s happened before in all kinds of aircraft.
I once had a jet ranger helicopter 500’ overhead nearly totally out of control. I thought it was mechanical issue. When it landed we found the pilot had a heart attack and was still barely able to land it.
But in this instance the pilot (while the other pilot was out of the cockpit) put the plane into a controlled descent at an angle which was consistent and according to several pilots would be highly unlikely in the event of a medical emergency.
Add to that the fact that this medical emergency just happened to occur when the other pilot was out, and further that the pilot in the cockpit took the plane off of autopilot, and how can one NOT come to the conclusion of terrorism?