I can't agree with this statement. Traditional narratives do indeed try to suspend audience disbelieve and make them feel part of the world the filmmaker is trying to create. Exactly the same is true of these types of found footage films. The only slight difference is that the narrative is of an amateur self-filming some real unexplained/unusual events. The world one needs to create in a found footage film is therefore one of apparent reality from the POV of our amateur's camera. But you're still creating a world and suspending audience disbelief to make them feel it's real, or at least real enough that they become emotionally involved it, just the same as with any narrative film.
In narrative film, the same as with any storytelling medium, what defines whether it is good or not is not so much the story itself but how the story is told and for me this my biggest criticism of this film. The actor presents the story in the style of a documentary narrator, not in the style of someone to whom these (apparently real) events are actually happening, which is fine for the introduction but not for the supposedly real time events. Too often when something happens there is either little/no response from the actor or a dispassionate third person narrator's type response and when there is actually some display of emotion it is mostly unconvincing. As a documentary it is far too slow to be interesting and as a narrative there is too little emotion or convincing emotion for the audience to empathise with or feel emotionally involved in.
Making a good found footage film might appear on the surface of it to be relatively easy, particularly as far as some of the technical aspects of filmmaking are concerned, but from the storytelling aspect they are actually very difficult to make well, at least as difficult, if not more so, as traditional narrative films.
G