Consider that, for somebody who has lived in the "Chinatown" section of any major city, a large percentage of the blacks they've met are of the "inner city" flavor.
As it happens, in San Francisco Chinese folks live all over town, not just in Chinatown. There are large middle-class residential neighborhoods where the plurality of residents are of Chinese ancestry, and there are Chinese people on the streets, in the shops, on the buses, and in the schools throughout S.F. Whatever it is that Chinese folks in S.F. think generally about black folks living here, it is not skewed by their having only limited exposure to the city’s residents.