Either he is pulling our legs that this a "Blair Witch Project" stun using Roswell or the man is very gullible and borderline paranoid to destroy the "evidence" of the case. I think it's a joke, a stun, and I honestly believe he may be laughing that a bunch of people here are taking it seriously and will read his book.
I agree 100% that it's a joke. He wrote it, of course, and the rest of it is just a typical literary stunt. I will explain.
There are a number of books that Spencer may be trying to emulate. "Pale Fire," for instance, by Vladimir Nabokov, contains an introduction in which the "editor," who received the manuscript of a poem, explains why he is writing endnotes and why he presents the poem as he does. It's a big joke, of course, and the editor, an implied author persona of Nabokov's, becomes a character in the story who is clearly insane. Similarly, Samuel Clemens wrote a book called "A Connecticut Yankee in King Arthur's Court" that the editor, the persona "Mark Twain," claims to have received in full. He, too, is simply publishing the piece to preserve it for posterity.
During the so-called romantic period, particularly the Gothic sub-genre, a number of authors did the same thing. They'd pretend to have received the manuscript from a person who received the manuscript from a blind man who dictated it to a little girl, for example. It's a very common literary device. I think that Spencer goes it a step further by extending the feigned editorship joke outside of the text and into interviews and real life. I really don't think that we're supposed to take what he says seriously at all. The guy is a novelist, according to what he says on the show, and it doesn't surprise me at all to see something like this coming from a novelist. My professional training has been in literary criticism and this makes me qualified, I think, to interpret the literary qualities of the book. My BA and MA are both in literature and writing. To anyone who has studied literature in great depth, it's pretty obvious that the entire thing is a joke.
All of this is, more or less, why I focused on the folkloric aspects of the book in my original post on this thread. It will be fun to watch how this story becomes a part of the Roswell mythos.