It's clear that it overheated badly, and there seems no reason to
suppose it was due to mistreatment as I don't think anybody's used it
anywhere near capacity.
The motor was very likely faulty. It looks a rather cheap-and-nasty
chinese unit, and they probably have a fairly high failure rate. But
the replacement wil probably be similar, if we know what to look out
for we might avoid another period of downtime.
It could have been a winding or insulation failure. There's not a lot
we can do about that.
Or it could have been a failure of the centrifugal switch as someone
suggested, resulting in the start winding being stuck on. If this was
the case, we might have been able to unstick it before it caused any
damage. We'd need to know early warning signs though. Did anyone
notice anything before the noises started ? It was probably too late
at that point.
Now is probably the best possible time to change the oil in the
machine, as it is due for that.