The aircraft entered a spin of some description, and as a result its forward, linear momentum, was transferred into angular momentum.
Whoa! Stop there. Let's take Occam's razor to this. Allow no other factors than the conversion of one...'display' of an aircraft's energy into another.
IF, this aircraft did suffer an conventional stall, much of it's forward energy would be lost before it hit the ground. I very much doubt that it would be converted into angular momentum, but dissipated into the air. Some of this would be immediately converted into heat, some of the remainder, would be expended by disturbing a mass of air, altering the water/vapor ratios, then more slowly converting into heat.
The rest, I would think a small proportion, would be converted into angular momentum.
Imagine this aircraft in space. A lamentable 134kts relative to a marker buoy. Now by some mysterious force, convert all of its forward energy into angular momentum and see just how fast the aircraft would be flat-spinning.