Not entirely true. The first people in Xinjiang are Tocharians(https://en.wikipedia.org/wiki/Tocharians) whose language is closest to Latin and modern day German and whose physique is most similar to modern day Nordic Europeans. They were mass genocided and assimilated by Turks and Uighurs in the 8-11th century. Iranians are Tajiks who only inhabit a tiny portion of mountainous Xinjiang near the Afghanistan border. The Iranian speaking Tajiks are close ally of CCP against the Uyghurs.
