The fire was set by a Toulouse Metropole truck, which spread to two cars 1m apart and which, given the extent of the fire, licked the facade of the building next door which was 2m away.
The other two cars, nor the building were targeted (although I will not regret the disappearance of two oil-powered cars).
The fire is not controllable once launched, be careful with the houses which would be close to targets.
Source: Attaque