When was it driven previously? How long was the drive?
I lost a car to fire, and then discovered my car parked next to it had the engine compartment full of dry, material for a birds nest. They had been packing the engine compartment with sticks, dry grass, etc.
I then looked under the hood of my Express van, and had four eggs in a nest next to the battery.
Lastly, I looked in my 2020 Silverado HD and they built a next in the front fender.
So I believe that the fire was probably caused by the heat of the engine igniting the dry material after it was parked.