material goods travel farther than the people who made them. And we are increasingly finding that it was the case that ancient and medieval trade routes were generally longer and more robust than we had once believed.
https://www.telegraph.co.uk/news/worldnews/asia/china/815449...
Why not? As far as I am aware it is a legitimate and decent journalistic news source. It might have a political leaning, but for this sort of reporting I don't think it would give their preferred political party and leverage.
https://en.wikipedia.org/wiki/Battle_of_the_Teutoburg_Forest
Further west along the silk road from Gansu, the earliest documented inhabitants of Xinjiang were the Tocharians. They had brown, red, or blond hair, spoke two different Indo-European languages (Tocharian A and B), and were Buddhist. They're a more likely source of blond hair in western China.
Quintili Vare, legiones redde! (Quintilius Varus, give me back my legions!)
Being blond haired and blue eyed doesn't mean much though since there are some non-European cultures where it exists. Solomon Islands people, and I've known blond Lebanese people, supposedly there are some blond north African people too.