Documents are classified at the highest classification of any single piece inside the document. In the cryptolog you linked to, there are two large redacted sections. It's not that the book review was classified, it was just published next to stuff that was classified. If you filed a FOIA request, they would have given you the book review with minimal fuss, but kept the redacted parts out of the FOIA. You can tell the information that is unclassified because it is marked (U). Classified info will be marked with different letters depending on the level of classification, and will likely be heavily redacted in anything released to the public.
