Jack's lighting of the fire in the forest was an act of savagery that likely would have smoked Ralph out and into his hands, but that also would likely have destroyed life on the island as they knew it. Thankfully, Jack's savage act did achieve the ultimate goal of the signal fire that was such a bone of contention between the boys from the beginning..... it caused them to be rescued. The boat sent someone over to investigate because of the fire, thus, I'd have to agree. I'd also have to say they got lucky, as things could have turned out far differently.