The missing puzzle piece here is that languages also imply APIs and Frameworks - which are beast in themselves. Rails is mentioned in the article. Understanding Rails, in context of a serious application, is a huge piece of work... And in many ways very different from knowing Ruby as a language.
If you're going to learn a language you probably want to learn a canonical framework for that language... which can be a much bigger (and maybe rewarding) process.
If you're going to learn a language you probably want to learn a canonical framework for that language... which can be a much bigger (and maybe rewarding) process.