10:1, this was a simple case of a mis-adjusted inner limit screw allowing the RD to engage a spoke. You may find evidence of this in the form of a bent or nicked spoke. Many people think of limits as set and forget, and in a perfect world they are. However the adjustment changes if the hanger is bent (always inward). Simple banging around, such as a fall on the right side can push the hanger in leading to the limit adjustment being too far inboard.

The other possibility is that the "B" screw was mis-adjusted so the upper pulley was too close to the cassette and engaged a sprocket (through the chain). This can push the RD back and in some cases break it off.