Well, I am certainly familiar with the rhetorical device of accusing your opponent of ignorance or stupidity.
So, what you are saying is that when Dan Brown writes in the front of his "novel" that "all this crap is true" he is just using a "literary device"?
What about when he continues to maintain that polite fiction in interviews?
Yes. Which is why the cover of the book says "a novel."
The rather simplistic device of claiming that a story is based upon "true" events ("only the names have been changed to protect the innocent" -- wink-wink, nudge-nudge) has been employed in everything from novels to comic books to television shows.
Surprisingly, it still seems to work.