Is “Declaring himself King of Yan and the meteor falling on the camp” true?
attested in history
The Records of the Three Kingdoms, Book of Wei, Biography of Gongsun Du records the process of Gongsun Yuan declaring himself King of Yan, Sima Yi besieging the city, and the meteor falling into the Liang River and killing Gongsun Yuan. The novel's plot closely matches the official historical records.
Gongsun Yuan
Both official history and the novel depict him declaring himself King of Yan, rebelling against Wei and establishing his own reign, and being killed while breaking out after a meteor fell on the camp when Xiangping fell.