This boy might jabe some mental issue, but

It might be triggered by his curiosity to play matches, not arson.  I read someone posted an extreme case about a teenage, I totally agree to keep alert and protective at any time, but I will recommend teaching this boy what stupid thing he was doing as a nice neighbor or a responsible adult. Calling police is simple, but most of time, this boy would be impacted by real criminals.  If he were your boy, what would you expect?