Since you still have the broken piston at hand, remove the piston rings and check their gap-width by putting them in the cylinder they came out off.
Maybe the engine-builder just forgot to gap the rings on this cylinder.


But then again, an engine with dyno-time only shouldn't eat a bearing like that already.
I think there has been an oil problem or perhaps dirt in the oil system during the mishap.
How do the other bearings look like?

Can you show a good picture of the top of the piston?