While taking a torque wrench to all 40 lug nuts on the bus is a bit of overkill, yes, it is important to check to make sure that at least that they are installed and in place.  As this was a rear dual tire (judging by the way the wheel was rolling down the road), the bus was able to come to a stop before a catastrophic failure.  Imagine what would have happened if it had been the front steer wheels that had fallen off! (enough said). 

Though quite dramatic and it certainly enough to make it on TV, the biggest danger was posed by the wheel rolling down the road uncontrollably.  Much heavier than a standard car tire, a commercial-grade truck tire that separated from a vehicle at speed is able to cause serious damage before it stops on its own.