If I remember the end of Bryan’s account correctly, he said that he wasn’t sure what was going on re: the abductions, but had concluded that there was a very real phenomenon (i.e., whatever it was, it wasn’t a hoax and it wasn’t mental illness).
That’s not how I read it. Bryan certainly allowed for mental illness as an explanation. I met him at a book signing and he made it clear he had no definitive answer but felt that a delusion of sorts combined with sleep paralysis could easily explain the reports.
In centuries past people reported seeing angels and saints. Alien abduction began being reported after the Foo Fighter reports at the end of WWII.