OMG!
Thank goodness no-one was hurt. Suspect it was the electrical wiring in the bus that 'caught' the lightning strike and caused the fire.
Generally, cars (and coaches) are good places to be during a storm:
Get inside a car if you can. Lightning will spread over the metal of the vehicle before earthing to the ground through the tyres.
Telegraph.co.uk:
How to stay safe in thunder and lightning3. School Buses. Metal buses are good Faraday cages. Make sure all windows are closed and the "hands on laps" rule is observed. Pull over and wait out the storm.
National Lightning Safety Institute:
Vehicles and Lightning"Hands on laps" = do not touch anything, especially anything metallic e.g. door frame, gear stick, foot pedals, cell phone charger.
Some potentially useful info in those two links.
NB: 'Soft tops' / convertibles aren't safe during a lightning strike.