Unfortunately, everyone is biased in some way or another. That mixed with your logic means the whole book is fiction, right?
The reality of it is that being biased doesn't mean you cannot make factual statements. It does mean you may highlight facts you want and ignore facts you find inconvenient. It also means you can lie.
In this case she is saying the author made statements of fact that were not true and is trying to point that out. As the book is an unofficial biography, you have to assume the likelihood of factual error is increased.
