It appeared to be a planned stall.. but I heard the engine sputter, not sure if the pilot blacked out (or maybe had heart attack?!).. but it appeared, to me, that there was little effort in recovering (hence, why I thought maybe a medical situation.. lack of throttle)..
FWIW my instructor taught me if I went into a spin to just let go of the controls if I did nothing else and if there was sufficient altitude the aircraft would recover itself since a spin is an induced maneuver that the aircraft has to be forced into (full aft yoke and full rudder).
I went on to fly Army helicopters so fixed wing was left behind but was I taught right about spins?
Anyway, a sad moment and prayers for the pilot and family members. Sickening to watch in fact.
My first thoughts as well, he blacked out.
God bless his family.