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.
Sorry but while what you state is technically correct you have no understanding of the laws that cover the pressure vessel mentioned here.
Way before they reach that point the pressure relief value will open and all the gas will leave the container to reduce the pressure to zero.
Surce: ME, 10 years as a Professional Firefighter.
Someone posted "Sparks from the breaks ignited gas tanks"
earlier. What I am thinking is the sparks ignited the fuel from the diesel tanks, and then the 02 cylinders (if they were present on the bus) suffered a catastrophic failure as a result of the heat.