Even though we cannot be certain of what Saki, the author, intended, we can surmise that the story ended with wolves for two reasons.
First, the story ending with wolves gives an unexpected twist. This makes the story more memorable. In the story, Georg and Ulrich hate each other. They are inveterate enemies. So, when they are pinned down underneath a tree and they become friends, it is unexpected. The reader, at this point, expects a happy ending, where two clans reconcile. So, when the story actually ends with the impeding death of both men, the reader gets a unexpected jolt.
Second, the ending begs the question of who really is the interloper. Is Ulrich the interloper? Georg? The point seems to be that both are interlopers. The wolves have more of a right to be in the forest than the men. In addition, by the wolves coming at the end, we are reminded of the beginning of the story when Ulrich wants to kill Georg for trespassing.