Within ten minutes it was fairly obvious that this was a mockumentary in a similar deadpan style to those of Christopher Guest, crossed with some improv in the vein of Curb Your Enthusiasm.
If the film-makers had attempted to keep it more within the bounds of possibility I feel it would have been more successful but I enjoyed the attempt nevertheless - as the film progressed believability was sacrificed for wackiness and holes in the stories that gave the game away that this was not, in fact, a documentary - I have a feeling this was deliberately referenced late on in proceedings when the filmmakers "interviewed" Elliot's put-upon girlfriend Linda, about the nature of documentary, with the fabrications of Elliot in regards to his past being linked to the fabrication of this film and documentaries as an entire genre.
I should note that very early on Elliot refers to Jean-Claude Van Damme as being French when he is in fact Belgian - this may have been part of his character's lack of depth in understanding but it was the first flag for me that made question this being a 'documentary'.