I think it' necessary to compare the right things together:
Ruby is a programming language; Rails (or better: Ruby on Rails - RoR, don't forget there's also Groovy on Rails - Grails) is a complete web framework including it's own persistency layer.
We absolutely agree. The title is just meant to draw in folks who consider themselves "Java programmers". In the book, we explicitly compare the Rails stack to the major players in the Java world: ActiveRecord to Hibernate, ActionController and ActionPack to Struts, etc.