I suspect the right front tire blew. I am only guessing but I suspect he was going 70 or faster. Just because the speed limit is 70 doesn't mean you are actually driving a vehicle combination that should safely be going 70.
On commercial vehicles (trucks/buses) they can not have re-treads or worn tires on the steer axles. Any violations on the steer tires will put them "out of service" until it is corrected. The video demonstrates the reason for these strict rules. A unit that heavy, going at that speed, is very hard to control when a steer axle tire blows.
I agree with what has been stated.....they were very lucky along with everyone else sharing that part of the interstate with them that day!