They're going to blame the wheels/spacers/lugs and anything that's not OEM first... whether it's warranted or not.
Looking at similar era chevy pickups, they looks like they have IFS. If the lugs failed I wouldn't expect the rotor to stick to the wheel, but it definitely looks like it's the rotor there, so it's tough to speculate exactly what happened. Someone has to have aftermath photos of the parts somewhere on the internet.
