Unreliable narrator

An unreliable narrator is a trope in which a fictional narrator cannot be entirely trusted. Maybe, in the story, he is telling events he did not watch happen first-hand, or he is deliberately lying about them for some reason (like hiding his own responsibility over negative outcomes, etc). An unreliable narrator is not necessarily malicious, but sometimes only mistaken, incompetent or misinformed - on the other hand, such a narrator may deliberately be lying and manipulating the audience for his own reasons, to the detriment of the truth and the public listening to it.

In The Beginner's Guide, Davey is an unreliable narrator, although this may only be apparent to some players very late in the game, if at all. He never truly explains his motives and players are never fully aware of the extent of his unreliability - which could easily go as far as to the entire story he is telling us being false, whilst he says otherwise.

The most likely explanation for Davey manipulating the narrative (in the context of the game, where he believes Coda to be real), is to more easily present to the player the same Coda that he envisions in his mind after his experiences with him. Whether this is malicious or not is up to debate - it being as harmless as just a person's take on a series of events; to it being as malicious as entirely misrepresenting a person to a huge audience worldwide.

Outside the context of the game, the most important assumption of Davey being unreliable is that the entire plot for the game is false and Coda never existed in the way the story upholds he did, and that all the game maps were created uniquely for inclusion on The Beginner's Guide in the months or years preceding its commercial release. This approach does not necessarily preclude the fact that Coda could still "exist" as a metaphor, as an entirely different person (or persons) or even as Davey himself (his younger self, a subjective part of his persona, etc).