Did Yuanchun write it himself?

Yes. According to a search on Bilibili, it was said in a TV interview that the actors all learned calligraphy, chess, calligraphy and painting before filming the TV series. Among them, the close-up of Daiyu writing about the stormy evening in the autumn window was Chen Xiaoxu's own calligraphy. "A Dream of Red Mansions" is a costume drama series adapted by CCTV and the China TV Drama Production Center based on the Chinese classical literary masterpiece "A Dream of Red Mansions". It is directed by Wang Fulin, starring Chen Xiaoxu and Ouyang Fenqiang, and co-starring Zhang Li, Deng Jie, Gao Hongliang and Guo Xiaozhen, with Zhou Ruchang, Wang Meng, Zhou Ling, Cao Yu, Shen Congwen and other red scholars participated in the production.