He speaks fluent English and German. It is eventually explained that he was, in fact, more high-born than the other laborers. But his views are as far from those of a high-born Cantonese of the time as they are from those of a Cantonese laborer. Another character considers the possibility than Sarah Canary is a vampire, having read some LeFanu. Yes, it is possible that someone might have read about vampires, but it is very unlikely and such a person would know other creatures of folklore that they would be equally likely to choose.
Fowler smugly pokes fun at all the strange and unscientific beliefs the man holds.
Of course, Fowler comes from a time when reliable scientific knowledge is readily and cheaply available. It is easy for her to laugh at the misimpressions of people who have not had her opportunities. Fowler's prose style is actually what attracted me to this book in the first place, and it is what I liked best about the book. She has a short, clean writing style. She never lets the writing get in the way of the story- telling.