There's an easy answer to that book: the author was an alien and sent here just to gin up that sort of misinformation. Let's hear what that expert of all things alien has to say about it:
Interviewer: So, Giorgio, what do you have to say about these stories that the aliens landed in N. Mexico at Roswell?
Giorgio A. Tsoukalos: Well, the aliens are known sneaks and liars, I wouldn't put it past them to plant these stories and then claim the aliens did it.
Interviewer: But....but if the aliens planted the stories, then the aliens are here among us, yes?
Giorgio: Don't be so sure, they could be only acting like they are here among us to fool us into accepting their kind.
Interviewer: Ummm....you mean cats are involved?
Giorgio: You didn't hear this from me, but have you ever met a cat who wasn't from an alien world? The feigned inability to open food cans so we'll do it for them, the total disregard for clear directions we give them, letting mice loose in the house so we'll think cats are worthwhile for us to provide a warm house and sanitary needs? C'mon, we're enslaved and they didn't have to fire a shot.
Interviewer: I can SEE the Light!!!
Giorgio: Thank you, thank you, my hair glows in the dark.