This is what they're referencing with that comment. I don't know that there's a "Japanese" style of Ruby, as much as there is a style that looks and reads more like systems code.
"The primary distinguishing characteristic of systems programming when compared to application programming is that application programming aims to produce software which provides services to the user directly (e.g. word processor), whereas systems programming aims to produce software and software platforms which provide services to other software..."
Reasonable, but I'm still not sure what makes code "systems code" or not, by that definition. Is it code that doesn't have a UI/display component mostly, as an observation that lots of Japanese Ruby programmers write code that's distant from the UI layer? Or something else?
https://github.com/ruby/ruby/tree/master/lib