Please explain what he could have possibly hit while on the interstate, headed to work this morning, that would have caused that? Another car, maybe, but I think he would have felt that.

If you notice, there is melting around the side-lug, that's now dissappeared.

Either way, we haven't been offroading for months, and he drives his XJ everyday to work and back. If it had been damaged the last time we went offroad, it would have blown out a long, long time ago, from the damage.

If he did hit something on the interstate, then their road hazard warranty should cover the cost, at least pro-rate the tire. But they aren't. They are sticking with the "underinflated" BS.

I've had blowouts from an underinflated tire before. It causes the sidewall to rip radially, not perpendicular. Only thing that'll cause a tire to rip perpendicular while driving, is a tire defect, IMO.