"Death in the Woods" ends with a reminder that most of the story we just read actually took place in the narrator's head.
True, the narrator did see an old woman's body lying in the middle of the forest, but that's about it. The "death ceremony" of the wolves is taken from a later incident in his own life (3.13). In fact, the narrator even implies that "Death in the Woods" is an amalgamation of a bunch of different stories he heard growing up when he states that "all country and small-town people have seen" old women like Mrs. Grimes (1.1).
With this established, the ending tries to show us why this brief moment became such an obsession for him. It certainly was a big deal at the time, but in hindsight he can see that he was "too young" to get "the point" (5.16). Which is a pretty weird way to look at things, when you think about it.
But the narrator views the whole experience as a sort of puzzle that's taken him until adulthood to solve. By mixing in his own life experiences with that of this mysterious old woman, the narrator is trying to make peace with the frightening reality of death and his own place in the world.