I would love to know all the particulars about this incident.
The chain failure looks like a classic case of mis-matched pitch to me.
I would bet a dozen donuts to a dime that the chain had gone past it's recommended elongation due to wear, or "chain stretch". I also bet that it was being run on a steel sprocket.
When we run a stretched chain on a steel sprocket, the integrity of the steel will not allow the mis-match of pitch to deform the teeth. Since there is a definate mesh problem when a chain stretches, the energy from the mis-match has to be absorbed somewhere. In this instance, it looks like the sideplates and bushings were the loosers in this battle.
One thing I can tell for certain is that this did not happen instantaneously. There was a period of time that the chain was run with several stress cracks before it failed. Just how much attention was paid to this chain by the owner?
I'm certain that general concensus may state that there was a mechanical failure due to a manufacturing flaw, but I bet it was more due to poor maintenance practice.
Unless I know for fact the procedures the user of this chain went through as far as cleaning/adjustment/lubrication, there is no way I would blame the mfg on this one.