alf5071h ..... and others here,
I realise that the concern about this incident is more about the particular aircraft and its low speed but I couldn't help noticing alf5071h's description of the aerodynamics (alf5071h - bear with me):
"When an aircraft is manoeuvred harshly nose down (a bunt), it reduces the angle of attack, which if this is less than the stall AOA, the aircraft will not stall irrespective of the airspeed."
I thought the lack of a stall here would have more to do with the bunt (i.e. negative G) effectively reducing the aircrafts weight (its mass remains the same). It weighs less for the period of the bunt which is why it doesn't stall at its normal level flight speed - it is partially ballistic for the period of the bunt.