In Chapter 4 of "Lord of the Flies," why is it ironic that Henry is "looking for a friend"?

In Chapter 4, Henry becomes absorbed in playing with small creatures in a tidal pool. Roger begins to throw rocks at him. Henry notices the stones and. at first he's concerned. Then, thinking it a joke, he looks for the "friend" who has thrown the stones. The irony is that it is Roger who is throwing the stones, missing on purpose, not because he doesn’t desire to hurt the boy, but because “Roger’s arm was conditioned by a civilization that knew nothing of him and was in ruins.” It is obvious Roger is no "friend" of Henry; he's just too afraid to hit him on purpose because of societal conditioning.