I assume you are responding to "Classes define new types" (correct me if I'm wrong). I did not intend that sentence to indicate that, therefore, classes are the only way Types are defined.
Saying "Authors write books" means that it is the job of an author to write a book, not that there are no other ways for books to be written. Poets write books, Editors compile books, but if I'm telling you what an author is, it seems fair for me to say that an author writes books.
Hope that clarifies, but if I've misunderstood you, please do let me know.