due to one engine spooling up more quickly than the other..
Yeah, who knows what the props were doing just before he stalled, presuming at a rather low power, and then maybe idle when he went over. PT-6's can spool up a little differently if you rush the power levers and things were not stable to begin with.
As for the DC-3, they have stall characteristics which must be understood, and trained, as the design precedes today's standards for handling. I have errantly done exactly what that video shows, during stall testing of a modified turbine DC-3, yes, it's a thing. Again, everyone crowded at the back of the cabin is terribly destabilizing, and a DC-3 is particularly vulnerable to this!