What does it mean that Du Fu has a younger brother named Duane?

Du Fu has a younger brother named Duane, a joke made up by netizens:

Du Fu has a younger brother named Duane. One night, a guest came to his house. Du Fu was so busy that he asked Du Fu to call Duane for dinner. So Du Fu shouted at the door, "Duane ~ Duane ~ Duane ..." Before he finished, Du Fu slapped him and said, "What is duang? Is that all you got to say You are duang. After a day, you are still duang. Are you bored? "

Du Fu (A.D. 7 12- A.D. 770) was born in Xiangyang, Henan, and Gongxian. [1-3] Shaoling Yelao, a great realistic poet in the Tang Dynasty, is also called "Du Li" with Li Bai. In order to distinguish Li Shangyin, Du Mu and Xiao Du Li, Du Fu and Li Bai are also called Da Du Li, and Du Fu is often called Lao Du.

Du Fu's influence on China's classical poetry is far-reaching, and he is called "the sage of poetry" by later generations, and his poems are called "the history of poetry". Later generations called him Du Shiyi and Du Gongbu, and also called him Du Shaoling and Du Caotang.