I think that there are two possible scenarios:
1. He simply didn't kill any of those people. Either he dreamed it up consciously or maybe while sleeping, and could not tell apart reality from this delusion of his. Thus he proceeded to tell the guy how he butchered all those people.
2. The exact opposite; he killed all of those people and the end was some sort of delusion or dream sequence. Sort of how when any one of us commits some sort of regretable act, we envision the way things would be had we not done such things.
1. He simply didn't kill any of those people. Either he dreamed it up consciously or maybe while sleeping, and could not tell apart reality from this delusion of his. Thus he proceeded to tell the guy how he butchered all those people.
2. The exact opposite; he killed all of those people and the end was some sort of delusion or dream sequence. Sort of how when any one of us commits some sort of regretable act, we envision the way things would be had we not done such things.