Why is Yang Xin called Uncle Wang Xianzhi?

Yang Xin is Wang Xianzhi's nephew. According to Cihai's website, Yang Xin and Wang Xianzhi are uncles and nephews. Yang Xin studied calligraphy with Wang Xianzhi. His official script, calligraphy and cursive script are all good. His name was very important at that time and was rated as "a wonderful moment". Yang Xin (370-442) was born in Nancheng County, Taishan County (now xintai city). Minister of Jin and Song Dynasties, calligrapher, son of Guiyang Taishou sheep.