I have no knowledge of this event, or flying this the Piaggio.
I wonder to myself if the use of reverse with an operating engine, whose propeller is so close to the rudder, makes things bad, when asymmetry becomes part of the equation. The propeller wash would form a blanking area which could really reduce the rudder affect, just when it's needed most. If reverse keeps the nose light (higher thrust line), the nose wheel steering would have little affect, leaving the rudder as the primary directional control.
I was right seat in a Piper Cheyenne 2, which was landed with one feathered, and some reverse on the other side seemed perfectly fine. But, that prop is a lot farther forward than that of the Piaggio, and perhaps the Cheyenne's disturbed flow from reverse has less affect on the rudder effectivness.
I have certainly experienced a loss of control affect with the use of reverse. You cannot hold the nosewheel of a Twin Otter off any more, when you apply reverse. The relatively high thrust line should help, but the affect is still there. The reverse makes the elevator hardly affective.
I wonder if the Piaggio specifies the use of reverse after an engine failure just below V1?