The Protocols of the Elders of Zion wasn't published as a novel, wasn't sold over the counter as a novel, and was never identified as a novel on its cover, in its pages, or by its putative authors. Rather dissimilar to the book under discussion, to say the least.
Der Sturmer Buchanan makes the same lame comparison of Elders of Zion to the Da Vinci Code.
As you mention, the Protocols were portrayed as being factual.
Buchanan has gone bonkers recently, says we now live in a "Satanic" society. LOL