What is so strange about Peter's photo that Ender sees in the computer game?

In Chapter Nine, the opening conversation is between Colonel Graff and Major Imbu, who seems to be the head of the computer system--or at least the fantasy game--at Battle School. Graff wants Imbu to explain why Peter Wiggin's face appeared in Ender's game scenario, but Major Imbu does not know; Ender is beyond the "End of the World," and someone else programmed the computer to go wherever it thinks best. Imbu suggests that the End of the World represents Ender's desire to end something about his life. Besides, the computer works to help, not harm, the players.