In my article, I specifically talk about Atlanta which is a "black city" as you term it. Atlanta is home to Georgia Tech which is one of the best engineering schools in the country. So it is strange to imply you wouldn't be able to find CS graduates there.
Secondly, companies have no problem opening engineering offices in China or India to chase after demographics so I find it strange that opening an engineering office in Atlanta is such an absurd idea that one must trot out the must played out racist tropes about black people.
http://atlantatechvillage.com/membership/current-villagers/
Eh? There are plenty of tech companies in cities with large numbers of African Americans. I'm just saying you shouldn't try to imply that 100% of Tech Companies should move to Atlanta (for instance) solely because there are a large number of black people there. You should be in Atlanta because it makes financial sense for the business you are operating.
I said it shouldn't be a criteria used to determine location. For instance, if you are doing eCommerce with a large import/export component, you are probably going to want to be HQ'd near a major port and you probably won't want to relocate any further than you have to (if you have to relocate at all) as a founder.
There are plenty of places on the West Coast where the largest minorities are Hispanic or Asian, they have easy access to factories in China & Mexico, and have small Black populations.
That doesn't mean they should relocate to Atlanta where they don't have physical access to the locations their merchandise enters the US.
The Bay Area is another area where this is an issue but it doesn't make sense to move (i.e. If you want access to Silicon Valley):
http://www.bayareacensus.ca.gov/bayarea.htm
The area is less than 10% African American. You aren't going to have more than 5-10% African American employees unless you are biasing things intentionally. The largest minority? Latinos followed by Asians.