Your quote is really ambiguous, I can't figure it out at all. Is there something wrong with Seattle black people? Surely not, but then just what exactly does that mean?
He means that the difference between white and black in america is magnified in comparison to the uk.
Whether you think it is true or not, I see the USA as much more segregated than Europe, and so the culture differences are exacerbated between the races.
Many black Americans participate in a different subculture than white Americans. They speak a different dialect, enjoy different entertainment, and have different traditions and values. This is largely due to centuries of segregation, and ends up reinforcing itself.
