206 has a sprag clutch.
Not sure what you mean as the explanation given is fairly good.
However, as the pilot increaced power the N2 speed would increace rapidly.
Suddenly applying this power when the clutch re-engaged caused a massive load on the drivetrain. The drive train in this case failed just below the head. That is a huge suprise to me (and I suspect to the pilot).
I would expect a failure either within the engine or main gearbox but more likely the freewheel or the engine to MRGB driveshaft.
As to your third question the answer would appear to be yes which is a touch worrying!!!!!!
I wonder if there is some other factor involved.
Could be that as they attempted to recover with no power available the RRPM had decayed so that when the engine re-engaged the differential between the N2 speed and RRPM was well beyond normal and the overstresss ocurred.
Still surprised at the failure point.