While in the air my RCS twin made a rude noise,and even though I cut the throttle immediatley and landed, the engine was seized.As it cooled off the engine would turn over but the compression was totally gone in one cylinder.Upon inspection I found three bad gouges in the piston and the ring came away in two pieces,but it had not rotated past the pin.The liner appears undamaged and there is no sign of over heating.The engine had been carefully broken in and at the time was running Klotz at 40/1.I do not run my engines lean and dont think this one was set too lean at the time.
What are the possibilities? Ill fitting ring? Foreign body sucked into the carb? Other Im not thinking about?
Also can this damage normally be fixed by a new piston and ring?

Thanks