Trying to pull on any one thread in this "book" is a fool's errand, be the topic Josephus or otherwise. It is a waste of your time. The book is broadly and comprehensively ridiculed in nearly every reputable arena. Atheists, New Testament scholars, Classics folks, history folks, Near Easterners, Hebrew scholars, skeptics, philologists, philosophers--everybody, essentially, gets a kick in. Polite reviewers call it "out there," while the more direct suggest that any undergraduate with any bit of proper training in source criticism and historiography can completely debase the entire premise after only a dozen pages or so. I've even seen the book used as required text in methodology courses specifically as a source of examples of what not to do. The basic premise does not even hold up under the most cursory scrutiny, using popular and easily-accessible primary sources like Tacitus or the letters of Pliny, much less more meticulous secondary scholarship. It's a hot mess. And by the way: if the Romans wanted to make up a mystery cult and foist it on their unsuspecting populace, they would have overwhelmingly chosen Mithraism, and it would not have taken three centuries to institutionalize it. The Imperial Court were experts at institutionalizing things, especially in religion, and they would not have needed vague references in Josephus to support their nefarious plot. Their actions would have been overt, heavy-handed, and clumsy. See, for example, the Aeneid and the latter books of Ovid's Metamorphoses. I would link a review from a reputable venue, but there aren't any--no one bothers. Robert Price will suffice, here.