Kate.. I fear you still misunderstand after 8 1/2 pages of explanation... His intent was to explain to the reader, who is a layperson how the word theory is used by the scientific community as opposed to how the layperson uses it. It is often confused.
In science, you aren't waiting for a theory to be proved.. It has been proven. It is not his personal made-up meaning. The title is not sarcastic. Often creationists try to use the argument that evolution is "only a theory" and thus has no proof... That couldn't be more untrue. The book is written for uneducated bums like me.
I'm glad to see you are reading the book, it is one of the best I've ever read. Enjoy :)