Without looking at the actual parts, perhaps the piston was made with a lower % of silicon. Therefore it tended to expand more than a stock piston. From the pictures I can't see that the ring fractured and rolled down the clyinder or that it hooked a port. From the limited information it looks like the piston may have expanded with heat, seized metal on the cylinder which then fractured the weaker grooved rings. The lower ring being the most beat up seems to support that theory.
Why hasn't anyone commented on the flow patterns on top of the piston? Again I don't have the cylinder in front of me, but it appears that the transfer port on the right side was angled a bit higher and being pushed up by the left side which caused a turbulence that curled the right transfer port towards the exhaust port. Granted, it didn't cause the seizure, but that kind of flow pattern isn't exactly conducive to good power.
If you ported those transfers, you should have noticed the pattern the first time you pulled the engine apart. If you didn't port the transfers, then that is a crap cylinder.
OK, I'm a new guy, I'll shut up now.
