Looks like classic detonation. On automobiles, too much timing or too low fuel octane will cause molten fragments to depart the piston and score the cylinder wall. If the ring was seized that was because of extreme heat. Look closely at the spark plug for silver deposits. That would confirm detonation. Maybe 100LL avgas or 93 octane auto fuel would have helped prevent this. If no avgas is available, mix auto fuel with 25% 110LL octane gas from a speed shop or 1/4 mile race track. That should raise the octane enough to prevent detonation. Perhaps the factory set ignition timing is off?...