Difficult stuff - from the NTSB Preliminary...
Whump Whump sounds like rotor blade slap from maneuvering.
Rapid intermittent popping sounds seems like a series of compressor stalls.
The positive coning angle on the rotor in the picture seems to indicate the rotor was turning at that point.
Flight trajectory became increasingly vertical could be the final portion of descent after speed reduction, powered or not.
Impacted the ground in a level attitude appears to indicate the very final portion of the descent prior to impact had rotor control for a flare?
A 4500fpm rate of descent is not normal for autorotation in an A-Star (or any other helicopter I am familiar with) unless possibly the rotor is at an adverse value. After impact the main and tail rotor blades apparently have little torsional/twisting damage. Not sure what that indicates.
Decades ago I trained pilots in the AS-350D and had them pick it up and set it down hydraulics off, prior to doing a circuit with hydraulics failure on downwind so they would have an idea what they were dealing with when transitioning towards the hover. This actually shortened hydraulics off training, and increased pilot confidence if necessary to make a hydraulics off approach to a point at such other than an airstrip, etc. The B series hydraulic off flight I am not familiar with; I suspect it is more unpleasant than the D-model.
Condolences.
WIII