Pictures indicate the bus was "burned" not blownup, oxygen DOES NOT explode, it only aids the fire's burning process, as in if there is no oxygen there is no fire.
A sealed pressure vessel will explode when heated to a point above the burst pressure of the vessel. This will make a very violent blast furnace.
"Oxygen does not explode"
True, but pressurized gas can explode -- without fire. When the gas is oxygen, and the tank explodes, it won't take much to get a fire going when the oxygen is released. Could have been an explosion and then a fire.