Why did Ralph get mad at Piggy?

Piggy interrupted Ralph, something he wasn't very happy about.

“Nobody knows where we are,” said Piggy. He was paler than before and breathless. “Perhaps they knew where we was going to; and perhaps not. But they don’t know where we are ’cos we never got there.” He gaped at them for a moment, then swayed and sat down. Ralph took the conch from his hands.