While I will admit it's possible the Raga had their own empire I'm not about to say that their Empire was the one that is called the Yokudan Empire. We have more sources stating the Left-Hander's empire was the one that spans four times bigger then Septim's whereas the book you presented does not state that, it doesn't even call the Raga Empire "the Yokudan Empire" it also makes no note of the Empire's size whereas we have an Ansei saying the Left-handers (left handed elves) had an empire spanning four times bigger then Septim's but said Ansei makes no note of how big the Raga empire was.

Yay racism.