Is “The Blue-Faced Beast Yang Zhi is a descendant of the Yang family generals, and because he lost the Flower and Stone Tributes and the Birthday Gifts successively, he was forced to become an outlaw.” true?

There was indeed a historical military officer named Yang Zhi. The History of Song mentions that he once followed the eunuch general Tong Guan on a campaign against the Liao dynasty and later surrendered to the Jin dynasty, making him a real military officer of the late Northern Song. In Chapter 012 of Water Margin, Yang Zhi claims: "洒家是三代将门之后，五侯杨令公之孙，姓杨，名志。" and also says "遭风打翻了船，失陷了花石纲，不能回京赴任". However, whether he was a descendant of the Yang family generals or whether he lost the Birthday Convoy and went to Liangshan are not recorded in the History of Song. The novel clearly borrowed the name of a historical figure and fabricated a story of his life in the martial world.