While I understand the point you're trying to make, OOP is a pervasive concept that should factor into building Ruby and RubyMotion apps. My point is if he opts not to use polymorphism in a RubyMotion app, it's an indication from him as the author of a RubyMotion book that polymorphism should be avoided for whatever reason (maybe the dynamic dispatch is too expensive). My assumption isn't that the author simply doesn't understand OOP, but rather that this was a deliberate decision. But, now a hole in his knowledge becomes best practice for many, because as you pointed out, it's the only book on RubyMotion.
I appreciate the humility. I just wish it manifested in a crawl before you can run mentality. There is actual value in understanding the fundamentals.
Instead, I found that he wrote from what I can tell the only book that introduces RubyMotion, published by PragProg, and endorsed by other authors.
His blog post shows humility, an ability to praise the work of others, and an effort to add value to the world.
All things that these HN comments distinctly lack and, ultimately, punish.