Of all the boys on the island, Piggy has the most logic and ability to reason. despite Ralph's optimism that his naval commander father will come to their rescue, Piggy's outward perception of events convinces him that dreams of immediate rescue are futile. He synthesizes three key facts about their crash before supporting this conclusion: 1) the plane crashed and the pilots are dead; 2)they did not arrive at their correct location, but were still en route over the Pacific; 3) He has reason to believe that every one may be dead because of the atom bomb war. Piggy's careful conclusion forces Ralph and the other boys to accept their situation and circumstances, so that they may begin to plan for a long term stay.
Piggy overheard the pilot of the plane talking about an atom bomb. So he concludes that everyone at the airport is dead and nobody knows the where the boys are.