Assuming that it wasn't shot with something, I'd guess it exploded when the rpm exceeded some rotational speed. Happens with grinding wheels occasionally.
Possible, but unless even the "normal speed" section of this video clip is slowed down severely, it doesn't appear to be going that fast. You can almost read the label as it turns.
That's why I think this exceeded rotational speed...the clip that I see looks like high speed video slowed down. You can see one here
