The complete quotation is "No. They're not as bad as that. It was an accident" (204). Ralph is referring to the group of hunters as "they" and is wrestling with the savagery and descent into darkness the hunters have sunk to. The pig's head is more symbolic and starts to twitch and move when the flies completely encompass it. The pig's head is a symbol for the darkness and savagery of the hunters. Ralph is trying to wrap his mind around the murders of Piggy and Simon. he's trying to figure out how and why the hunters were capable of such beastly acts. He's also thinking in terms of his self preservation. Would they be capable of doing the same to him? Ralph is trying to persuade himself that there's still some goodness and compassion in Jack and the hunters. There probably isn't.
In chapter ten Piggy wrestles with the murder of Simon and tries to explain it off as an "accident." Ralph says, "that was murder," yet Piggy tries to justify the "accident" by saying Simon shouldn't have crept up in the darkness like he did.
At that point Ralph knows it was wrong and murder, but it is not until chapter twelve when his psyche tries to process it.