Dear Judy,
According to all of the sources I have checked, there never existed a documentary named “The Navidson Record.” You bring up an important point – if the Navidson Record does not exist, then the premise of House of Leaves becomes unreliable. It is fiction, though, so ultimately it is the same with any novel.
I would guess that the author created this novel as more than just an unusual book, though – I think he wants the reader to ask many questions, such as “What is a novel?” and “How do we decide what things mean?” It gets pretty deep, which is probably why your son has assigned it to our class to study.
I hope you enjoy the book!