In chapter 12 of Lord of the Flies, why does Ralph feel he's been targeted?

Ralph sneaks down to the camp at the Castle Rock and finds Sam and Eric guarding the entrance. The twins give him food but refuse to join him. They tell him that Jack plans to send the entire tribe after him the next day. Ralph hides in a thicket and falls asleep. In the morning, he hears Jack talking and torturing one of the twins to find out where Ralph is hiding. Several boys try to break into the thicket by rolling a boulder, but the thicket is too dense. A group of boys tries to fight their way into the thicket, but Ralph fends them off. Then Ralph smells smoke and realizes that Jack has set the jungle on fire in order to smoke him out. Ralph abandons his hiding place and fights his way past Jack and a group of his hunters. Chased by a group of body-painted warrior-boys wielding sharp wooden spears, Ralph plunges frantically through the undergrowth, looking for a place to hide. At last, he ends up on the beach, where he collapses in exhaustion, his pursuers close behind.

He is the only "enemy" left.