If the ring gap was too small then here is what is likely to happen:
When you first start up it would be great. In fact, the small end gap gives you an even better seal, best possible performance.
As the piston/ring heats up, however the thermal expansion causes things to grow. The ring gets bigger, and the end gap decreases. As long as there is still some end gap things are good.
Then you get to a stretch where running the engine for a sustained period at high RPM and WOT. Now the piston heats up a lot and the ring grows to the point that the end gap closes down to zero. Any further expansion and the ring is being forced into the cylinder wall.
This added force against the cylinder wall creates a lot of friction, which only heats the ring more, adding more pressure, making more heat, causing more expansion, more friction, and the cycle continues.
The increased friction means less power, which you may have noticed as you were riding. The increased heat is also doing bad things to the piston and possibly cylinder and head. If the heat builds up to the point that things start to melt then it is possible, likely even that the piston jams into the cylinder and siezes to the point that it won't rotate anymore.
Your's may not have made it to that point. The piston may still be intact without any holes or significant distortion. The ring may not have fared so well.
I would guess that the partial seize has scored the cylinder wall lightly and made the ring such that it doesn't seal any more. I will modify what I said earlier, you should remove the cylinder and replace the ring. When you replace the ring you will also be able to inspect the piston and make sure that the groove that the ring rides in hasn't collapsed.
Rod