What is the content of the allusion to Feng Jing being mistakenly attributed to Ma Liang?

Feng Jing, a real person in history, was from the Song Dynasty. But I didn't find the exact starting point for the allusion of "mistaking Feng Jing for Ma Liang".

Generally speaking: During a provincial examination, a certain examiner was so dim-sighted that he put the two dots on the left side of the "Feng" surname of the candidate Feng Jing onto his name. One person should answer. This is the joke of "mistaking Feng Jing for Ma Liang".

"Mistaking Feng Jing for Ma Liang" means that you have mistaken the wrong person.

Information about Feng Jing:

Feng Jing (1021-1094) was born in Xianning, Ezhou (now Xianning, Hubei Province) during the Song Dynasty, and later moved to Jiangxia. He was the son-in-law of Fu Bi, a famous prime minister in the early Song Dynasty. In the first year of Huangyou (1049), Ji Chou passed the exam with "Sanyuan". He successively served as general magistrate of Jingnan Prefecture, Zhiji Xianyuan, magistrate of Nancao of the Ministry of Civil Affairs, and a bachelor of Hanlin. He successively knew Yangzhou, Jiangning Prefecture, Kaifeng Prefecture, and Taiyuan Prefecture. After Shenzong ascended the throne, he became the censor Zhongcheng, and moved to be the deputy envoy to the Privy Council and to participate in political affairs. . He opposed Wang Anshi's reform, and the two often argued in front of Shenzong. He strongly recommended Su Shi, Liu Tong and others. Therefore, in the eighth year of Xining (1075), he was dismissed to participate in political affairs and went out to Bozhou. Later, he served as the governor of the Baoning Army and changed his name to Damingfu and Zhangdefu. In May of the sixth year of Yuanyou (1091), he became an official as Prince Shaoshi. He died in the first year of Shaosheng (1094) at the age of 74. Zhezong personally went to his home to pay homage and presented Sikong with posthumous slips.