That sucks!
My guess would be the belt slipped, the valves hit the piston, cam tried to push valve down more, cam took the torque & snapped along with the belt.

When you take the head off, I bet you have a fair amount of bent valves & makes on the pistons.

 

Cam broke that does suck I havent seen or heard issues of that sort keep us updated on progress

 

Discoloration on one side and not the otherwould indicate overheating. I would imagine the cam issue is a symtom of a different problem like oil starvation on that side, possibly a blocked oil journal? I would have the mechanic make sure nothing else has caused it.