Well it wouldn't be the first time the show did something like that. The very first scene from the pilot is pretty much a self-contained, thematic jumping off point for the entire series that's otherwise placeless in the chronology of the story.Quoting Qrazy (view post)
Sure they haven't done anything like it since, but the considerable variation in the two versions of the scene, with the shin-punctured kid heading for the knife sooner the second time around, led me to believe in the moment that they were doing something out of the ordinary with it.
And yeah, the ending was fantastic, as was the reflection he saw of himself that turned into the reveal of the walkers in the building.