In Chapter 10, Golding is bitterly ironic:
Memory of the dance that none of them had attended shook all four boys convulsively.
At first, Ralph openly admits that they murdered Simon. He does not deny the truth, and his guilt overwhelms him. He keeps asking Piggy if he saw what was done to Simon, what they all had done to Simon. But Piggy will not let him confront this truth. Piggy tells him
"That's right. We was on the outside. We never done nothing, we never seen nothing."
When the twins arrive on the scene, they claim that they left early. At that point, the boys stop speaking and the memory of Simon's murder overtakes them.
But Ralph was there, and he remembers that Simon "said something about a dead man." And he somehow remembers the "ungainly figure on a parachute." So, Ralph does know the truth of the beast, that it is a dead man on a parachute. Not only has Ralph participated in the murder of Simon, but he has also participated in the fear-mongering that has engulfed the entire island. He let himself believe that there was a beast when he now knows what he really saw come from the sky was a parachutist and what Simon was trying to tell them about the "dead man on the hill."
Lord of the Flies is a symbolic novel in which the people, places and characters have meaning beyond their actual existence. In chapter ten, the boys have just woken up the morning after they killed Simon in a stormy, beast-killing kind of ritual. They're reluctant to talk about it, of course, or even to name it for what it was--murder. In the course of this chapter, Ralph begins to reflect on what has happened and on what Simon had said to him over their time together on the island. We read:
Ralph remembered the ungainly figure on a parachute.
That's what he remembered seeing. What he remembered Simon saying was this:
"You'll get back to where you came from.... You'll get back okay. I think so, anyway."
Simon, symbolic of the conscience or the spirit, told Ralph he thought he'd be okay at the end of this ordeal. When life on the island is worst for Ralph, this is what he remembers.