the chainsaw guru strikes again. What do they want for a DR kit piston on treats? $100? That chainsaw piston looks pretty much the same.
ok here's my theory. Could be completely wrong. I think the piston did get hot, swelled up slightly but not enough for a soft seize. One of the rings bulged into the exhaust port and caught momentarily. Probably did this more than once until it broke - most likely as the piston was going down. Broke part of ring got caught ahead of the piston and the damage to the piston was caused by the piston driving into the broken ring on the upstroke.
anyhow, if it were me, I'd hone the cylinder and throw in that chainsaw piston and give it a whirl. (edited)