I saw that and thought he was talking bollox actually. Because the most common usage of the two words is that authors write books and writers write anything. So someone who journals, or writes for magazines or newspapers, like me, is a writer. I also have books. I've authored those books - because that's what authors do - they write books. But the term author is also sometimes used for research articles, or other works, so there's some flexibility around how they're used, and I guess different people will have their own definitions.