Impressive.

I would agree, your drum probably seized, or became high friction, and the motor pully slipped on the belt and melted itself. It may point at the machine having been overloaded, or the drum bearings failing. The belts have a remarkably high destruction temperature, I once managed to do something similar with a cast aluminium pulley on a 4 horsepower petrol engine, and the pulley actually melted before the belt snapped!

Looking at the middle picture, the shaft has a groove machined around it near the end that small plastic tangs from the pulley snap into to stop it coming off. I would imagine that the shaft is keyed in some way to stop the pulley rotating on it. If you break or cut off those tangs, the pulley will come off much more easily. It may even pull off with hand pressure.

pca