Catastrophic indeed! Usually a broken motor mount is associated with the rubber portion collapsing. In your case, it seems that the bolt connecting the mount to the engine broke or loosened, or the smaller bolts holding the mount to the frame did the same. Or the rubber portion cracked enough to allow the large bolt to have just enough slop to allow the engine to move that much while under torque.

I would also scrutinize the transmission mount.

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