Interestingly, during the "spin" the indicated airspeed increased from 62 knots to 140 knots, which doesn't actually sound like a spin. The vertical speed also increases with the airspeed.
140 knots with between 50 and 70 degrees pitch down would indeed give an impressive rate of descent.
Quotes from the POH in the report:
"In some cases it may be difficult to determine if the aircraft has entered a spiral or the beginning of a spin."
and:
"if the aircraft enters an unusual attitude from which recovery is not expected before ground impact, immediate deployment of the CAPS is required"
Good advice
It sounds to me like the PIC/salesman was (as he noted) "overconfident as he had done the demonstration 30-50 times" previously and unprepared for the resulting unusual attitude.
I don't believe it was an actual spin due to the steadily increasing and resulting high IAS value. It looks like a spiral that possibly it could have been recovered by closing the throttle, rolling wings level and pulling out of the dive. That may have been difficult due to airspeed/G/altitude limits.
The CAPS certainly saved the day, and the PIC made the correct decision following the loss of control.
I don't think much blame can be put on the aircraft here, except perhaps for inducing overconfidence in the pilot. Might similar performance aircraft e.g. a Bonanza also occasionally drop a wing and enter a spiral if you did a similar stall (25 degree bank, flap, adding power as it stalls)?