If he really did throw light up cigarettes whenever there's grass and lots of trees, then he may have caused some of them but some forest fires don't get caused by light up cigarettes. Some of the deadliest fires were actually caused by pyromaniacs, who stalked people from one place to another till they reach their home. They will then enter their house, cause the fire inside there and since they enjoy playing with fire, they may even stay there absorbing in it, ( though it may be possible that this will happen if this would be the fire that lead to one's death, ( suicide instinct ). If not, they will just look at it. However, a true forest fire is probably caused by something far more dangerous than a cigarette, the only one i can think of is gasoline or something else like a flamethrower.