Are the people of Shaanxi descended from the Qin people?

Probably not. Even if there are, they are not purebreds, they are all mixed-races. Shaanxi has been repeatedly invaded by foreign tribes since the Han Dynasty. A large number of ethnic minorities have migrated inward. They have intermarried with the early Qin people. They are definitely not pure Qin people. For example, during the Wei, Jin, Southern and Northern Dynasties, many ethnic minorities established political power in Guanzhong. The famous ones like Fu Jian of the former Qin Dynasty was a Di people. He destroyed the former Yan and Empress nearby and moved a large number of Xianbei people into Guanzhong. Most of the Murong clan of the Yan king settled in Shaanxi. They must have become mixed in the end. After that, there was the Later Qin regime that destroyed the Former Qin, and it was founded by Yao Chang of the Qiang ethnic group. The last Xianbei regime to unify the north, the Northern Wei Dynasty encouraged intermarriage during the reform period of Emperor Xiaowen. It is conceivable that the Shaanxi region, where there are a large number of descendants of ethnic minority nobles, did not know how mixed they were.