There was no attempt made to use Ruby idioms in the article. I think you're missing the point. It was merely an example how one can use alternate build tools, while extending their JavaScript or Cordova based app using Ruby over Objective-C. Not everyone is a fan of Xcode nor Obj-C. Lots of education about the tools was included to help one get on their way; the intention was not to be craft a reason as to why Ruby idioms can make a developer more productive.

RubyMotion does make sense here, if your goals are as described in the article.