The outer part of the rotor is fused right into the caliper.. What's more remarkable is the inner part has broken free from the outer - see the clear line half way along the surface of the rotor? This allows the wheel to spin somewhat freely now. It's not clear whether it was like this ahead of time or it was slightly jammed. The friction would have turned it red hot for it to break like that - enough for the grease in the hub to catch fire. The tow driver actually confirmed it appeared to be coming from the hub, not the tire.
I feel the tow driver has no fault in this. There was no way for him to know this was going to happen.
So one thing's for sure.. This bus will need a new tire, new rotors and pads, and most likely brake calipers. I will need to do a full inspection on the brake system to come up with a list.
I stayed home tonight to receive the bus. Tomorrow is a VW camping event. I should get a chance to look into this further on Monday so we can get the parts on order.