Shytorque,
Not to deminish your event too much, but I bet it was a failure of that collective pot, so that it basically beeped the engine up to high N2, but not semi-permanently to maximum power. Perhaps I am wrong and it was a true worst case runup to full power. The max beep event is alarming, but just (in the end) a runaway of the N2 set. A true high side failure makes the engine go to max power, which would, while at flat pitch on the ground, probably trigger the overspeed protection as the way to protect the aircraft.