I think some of these aren't North Korean-authored, but international textbooks in unofficial translation. For example, Google matches code samples from "CTBooks1/ANSI_C++.pdf" to this textbook from 1999 (and the front-cover graphic is identical), https://books.google.com/books/about/Object_oriented_Softwar... I think the version they're translating is a UK print edition, because the currency unit in the code is "£".…
I would assume they copy Chinese textbooks as it's the only border. I wonder if, when discussing ANSI C++, they admit what ANSI means.
And their CS majors supposedly have monitored but uncensored access to general internet. I'm sure they know that the A in ANSI means American.