So both are diverse and have large foreign populations. But SV’s diversity largely comes from immigrants in search of the American Dream, most of whom tend to have affinity with the rest of America as well.

Manhattan in contrast has a lot of global citizens who would have more affinity with other cosmopolitan cities like London and Paris than with the rest of America.

This is a huge generalization and a guess on what it means. If you are in tech, looking to live in the US from abroad, some really only consider moving to NYC or maybe SF, LA or DC. Then once in the US, you don't really ever get a feel for living anywhere else in America. Whereas US born citizens living in NY or SF probably grew up somewhere else, so they have more of a connection with the rest of America.