Good summary, but it doesn't quite make it clear what safety device failed. The firing pin block exists to ensure that an impact in-line with the firing pin can

Good summary, but it doesn't quite make it clear what safety device failed. The firing pin block exists to ensure that an impact in-line with the firing pin cannot move it when the trigger is not depressed. It too could be moved by inertia, but its movement is perpendicular to the firing pin itself, so an impact cannot move both at once. In this case, the magnetic field moved the firing pin block, while inertia pushed the firing pin forward relative to the rest of the gun. This is the only time I've ever heard of a firing pin block failure resulting in an accidental discharge.