What does Cao Cao mean about Guan Yu's kindness in the 50th chapter of Romance of the Three Kingdoms?

In Romance, Guan Yunchang was persuaded by Zhang Liao to "temporarily" surrender to Cao Cao (once he learned that Liu Bei was still alive, he would go to defect), and Cao Cao had the grace of not killing. In Cao Ying, Cao Cao was meticulous about Yunshang, sending money, officials and beautiful women, and even generals such as Chu Xu were jealous. When Cao Cao left, he said goodbye to Yunshang, and Yunshang was more or less grateful.