In order to answer this question, some background information is necessary.
Right from the beginning of the story, the narrator introduces a family feud. The Gradwitz family and the Znaeym family are feuding over a tract of land. The land is not very good, but they are fighting out of hatred, rivalry, and pride. The court ruled in favor of the Gradwitz family, but the Znaeyms would not accept it.
After two generation Ulrich von Gradwitz and Georg Znaeym are still fighting. Ulrich and his men are in the forest for one reason. They want to guard the land from Georg and his people. Ulrich even wants to kill him. Ulrich considers Georg an interloper. According to the text, there was real animosity. The men hated each other. The language that Saki uses is strong:
The neighbour feud had grown into a personal one since Ulrich had come to be head of his family; if there was a man in the world whom he detested and wished ill to it was Georg Znaeym, the inheritor of the quarrel and the tireless game-snatcher and raider of the disputed border-forest. The feud might, perhaps, have died down or been compromised if the personal ill-will of the two men had not stood in the way; as boys they had thirsted for one another's blood...
The irony of the story is that they become friends, as both men are pinned down under a felled tree.