There is no official information yet. However, two things to note:
1. This was a flight with two very experienced instructors, presumably doing some continuation training exercises.
2. The crash site photos imply an almost vertical impact with little or no pitch angle. I remember seeing confirmation of this somewhere else. The second photo I posted shows an impact scar which might indicate rotation, but it might also have been caused by the wreckage sliding downslope.
I've not been able to find any information on stall-spin Tecnam twin accidents.