Note I apologize if anything I say sounds like it is motivated from racism. It is not my intent to stir up controversy but to explain things so that both sides can better understand each other.
The Chinese diet may have been a cause of prejudice against them in the nineteenth century. The smell of Chinese grocery stores and restaurants was offensive to the Western nose. And it was highly likely that rats were part of the menu. That’s because rats and mice were and are commonly consumed in China. And also because the animals would have been plentiful in a time when the Chinese were experiencing great poverty. I have not been able to find any source that says that rats were part of the Chinese diet in the 1880s, but the stereotype was definitely there.