Copypasting from my blog some extra info about Lord Mengchang:
The actual Shiji has a slightly more negative portrayal of Mengchang. For instance, after he successfully escapes Qin, he crosses through Zhao to return to Qi. However, some Zhao commoners who came out to see what the great Lord Mengchang looked like as he passed through their town, they burst into laughter because his physical appearance was that of a small and unimposing man. Lord Mengchang was enraged by this, and his guests drew their swords and killed several hundreds of people, destroying an entire county. This incident somewhat goes along with the fact that there were more than a few ruffians among Lord Mengchang's many guests.
In fact, Sima Qian even concludes his biographical chapter on Lord Mengchang by saying he personally visited Xue and found that its customs were rough and there were many violent youngsters, quite unlike the hometowns of Confucius and Mencius. Sima Qian asked a Xue resident why there were so many rough men, and the resident replied it was because Lord Mengchang had invited both stalwart and despicable people to the point that Xue had grown by 60,000 households during his rule. Thus Sima Qian remarks that Lord Mengchang being fond of receiving guests was at least one rumour about him that wasn't baseless. Overall, Sima Qian seems to view Lord Mengchang's generous reception of shi as mostly positive, but was more critical towards his lack of discretion and judgment towards those shi. Given Confucianism's central emphasis on cultivating morals in oneself and others, it's not too surprising that other writers echoed similar criticisms. The famous Song dynasty Confucian bureaucrats Wang Anshi and Sima Guang may have been bitter political rivals, but both negatively viewed Lord Mengchang, with Wang Anshi calling him a leader of ruffians, and the Sima Guang calling him a hero for villains.