this line from the article explains why

Posted by exer on May 11, 2006 at 15:37:30

In Reply to: Christian Foes of 'Da Vinci Code' Mull Tactics posted by moonshiner on May 11, 2006 at 14:57:38:

"The Da Vinci Code" was marketed as fiction, but Mr. Brown said in a preface page that his descriptions of artwork, documents and rituals "are accurate."