To Liu Bu, Luo Xinyu, and the others who lived in the stronghold, a rat was synonymous with dirtiness. Traditionally, they were creatures that scuttled around in the sewers and represented plague, disease, miasma, and so on.
Although Ren Xiaosu also did not eat rats, it was only because he had seen them feeding on carrion before. It left a terrible impression on him. But to the other refugees in town, their natural mindset was that rats in the wilderness were food all the same. These rats stole food from humans and even preyed on other living creatures, so there was no difference between them and any other wild animals.
Since there was a shortage of food in town, they would even turn to eating termites, not to mention rats. This rat would look just like a walking piece of meat to them.
Compared to those in the stronghold, the refugees' perception of food was different. The refugees felt that anything could be eaten as long as it didn't kill them.