Why is Wu nicknamed "Wu Xiaogui"?

"Cao Kun played the old section and Wu Xiaogui went to the front line." "The gun of the organ is crisp, and Wu Xiaozi hit Duan Ruiqi." It is the Zhuozhou folk song circulating in this era. Wu is a general under Cao Kun. He is short, good at divination and scheming, and stands out in the melee between warlords. Because this Wu was brave and heartless during the war, he was nicknamed "Wu Xiaogui".