What is the reason why Guo Gongsun knows Niu Buyi?

Guo Gongsun knew that Niu Buyi was Guo Gongsun's matchmaker. Guo Gongsun and Niu Buyi are from The Scholars. Niu Buyi visited Lou's two sons. The two sons warmly hosted Niu Buyi and told the story of their stay in Beijing. Later, Niu Buyi and fortune teller Chen Hepu became matchmakers between Guo Gongsun and Miss Lu, and they swam together in Yingyi Lake.