Intermarriages have contributed to mixed population. During Tang era while China was very powerful and rich, more and more foreigners came and lived here.
Too many such examples. In west HeBei, ancient ZhongShan Guo/State people were from East Euro (based on Chinese history records) so they have some Euro/White genes which is very common. One of my friends is from that area and his generic test shows some weird results - some Euro nationality gene.