I was told the aircraft reached a point over 490 Rpm, I'd expect that a B3 runs at 390 +/-, similar to a B2 ? So that equated to a 126% M/R speed.
An overspeed can happen to any aircraft.
If a FADEC or governor system goes bad, Zoom, up comes the M/R RPM.
The pilot controlled the overspeed, (or it went into an automatic shut-down situation, I'm not familiar with the B3 systems), he auto'd and all 3 on board are fine.
The aircraft can be repaired.
Well done !