Neighborhoods being segregated is much more different than entire geographical regions. People in those neighbourhoods still travel around. Also, Rosemead's most populace race according to wikipedia is only 60% asian. That's a far, far cry from 80-90+% white regions.

(I should also note that the idea they wanted familiarity is just one part of why specific minorities live together. Another is because of the effects of racism actively rejecting any attempt to integrate.)