It looks very much like flying 'on the wrong side of the drag curve' this is a stable state and if your aircraft has sufficient power then the lift is supplemented by the power from the engines as they have a significant upward vector due to the nose high angle and the aircraft will happily fly straight and level at below its normal stall speed 'sitting' on the power. Can be fun if you can see what you are doing.
If the aircraft is at height and power to weight ratio is not good or power is reduced the aircraft will drop - quite fast - as AF447 did. The nose high attitude must be maintained and for that the tail plane had motored into full nose up 'trim' - and every throttle increase with underslung engines also assisted the nose up attitude. This is not a classic stall.
The aircraft is now in a stable nose high state dropping faster than its forward speed. Unwittingly, PNF by insisting that PF kept the wings level assisted in the maintenance of the stable state. Had PF lost the roll control the aircraft would have rolled out of its stable state - perhaps before the tail had motored to full NU. That would have provided a more 'conventional' LOC that they may have recovered from. As it was they sat on the wrong side of the drag curve all the way to the surface.