Did you notice I didn't talk about paint? Some paint was spilled and so some kids must have started a fire? What's the logical connection? There is none.
The rubber fire was spontaneous combustion. The fire marshal is no scientist, and neither are you. For that matter, a decent fire marshal ought to be aware of the long and dire history of spontaneous combustion in stored rubber. You can be excused on account of acute ignorance.

Here, read this, dummy: http://www.hse.gov.uk/rubber/spontaneous.htm