From what I understand, it wasn't the bus company's fault at all. The explosion happened because of the the oxygen containers belonging to some of the patients. I don't know what caused them to blow, but AFAIK, it didn't have anything to do with the bus, the bus company, or the driver.
Yes, you are correct - you don't know what caused this fatal fire. One thing is for sure, it wasn't the Oxygen containers. Apparently you don't know much about combustion or oxygen containers either.
there needs to be an exposed fuel source (gasoline) and a heat and/or spark in the presence of an oxidizer (fresh air will do.)
The Oxygen bottles were caught in the fire as were the patents. Upon being consumed in the fire, the plastic tubing carrying the Oxygen caught fire and/or melted exposing the fire to a steady stream of pure Oxygen, thus increasing the temperature of the fire, which eventually consumed the Oxygen bottle melting the valves, thus releasing a burst of the bulk of the Oxygen making the fire burn even more intently.
The short answer is that the Oxygen canisters did not cause the fire (no matter how much the lame-stream media tell you so), but having the Oxygen canisters in the middle of a fire sure made it a more intense fire, that combined with immobile riders and insufficient assistance, turned deadly.