What was ironic/funny about the fight in the dark on p149-150?

In chapter 10, Ralph, Piggy, and Samneric huddle together in their shelter to sleep and are awakened in the middle of the night by Jack and his hunters. Jack and his hunters attack Ralph's tribe, and the boys wrestle each other in the dark. During the fight, the boys cannot see who they are fighting against and randomly punch, scratch, and bite each other. Ralph ends up sitting on someone's chest and begins punching them in the face. Suddenly, Ralph gets kneed in the groin and doubles over in pain. Shortly after rolling over in pain, the shelter collapses and the boys realize that they've been attacked by Jack and his hunters. As the boys discuss the fight, Eric mentions that one of Jack's hunters was beating him badly but claims that he got the better of him in the end by kneeing his enemy in the groin. Ralph then notices that Eric is playing with a tooth that has been knocked loose during the fight. It is humorous and ironic that Eric believes he was fighting Jack or one of his hunters when he was really fighting Ralph, who is his ally. The fact that Ralph and Eric were both fighting each other is ironic because they are friends and were attempting to harm Jack and his hunters.