WHY is anyone surprised about this. China has been doing this,and worse,ever since there has been a China.
If one looks at a map of China showing provinces one can notice that around the periphery of just about all but the coast are various ethnic-group "autonomous regions". Inside that periphery is the historic core of China, and those "autonomous regions" are ethnic groups with which dynastic China was variously, controlling, raided by, and even ruled by (the Mongols ruled China for a century or two, and the Qing dynasty - China's last dynasty - was Manchu, not Han Chinese). In modern China, in ethnic-group "autonomous regions" those ethnic groups are, in varying degrees, oppressed, and the long-term policy is Sinicization, extincting those ethnic group's languages and cultures.
Of the several "autonomous regions" the two that, over the centuries, were least often under Chinese rule are Tibet and Xinjiang. Guess which "autonomous regions'" ethnic groups are most oppressed.