I see flat spin transitioning to normal spin, and thereafter pro-spin controls (out-of-spin aileron, stick back, into-spin rudder) were held for many rotations. Perhaps the pilot didn't believe the flat spin had stopped. The spin finally stops and the aircraft starts to fly near the end but far too low for a recovery. If the pilot was trying to recover from the spin at any point why wouldn't the stick be put forward and the rudder applied out of the spin? Either one of these would stop the spin on most aircraft. The only explanation is that the pilot wanted the spin to continue for some reason. Incapacitation doesn't seem likely, because all three controls would likely not be held pro-spin if, for example, the pilot passed out.