Japanese from the main islands don’t consider Okinawa Japanese as “pure” Japanese. Rural people don’t usually mix with city folk.
All true. But unlike the usual “racist!” epithet Liberals throw out when they feel the ground beneath their arguments give way, I and most if not all of us who are using the term here mean it in a neutral and purely descriptive sense. It’s just how the Japanese are and they’re not inclined or likely to change.