The author simply doesn't know what segregation was at all. If all the black people lived in one neighborhood and all the white in another, and they never cross

The author simply doesn't know what segregation was at all. If all the black people lived in one neighborhood and all the white in another, and they never crossed, why would you segregate bathrooms? And restaurants? And water fountains? And schools? And busses? Housing was already integrated and the services were segregated on skin color. That was one of the quantifiable objections to segregating school other than the obvious moral reasons - the students had to walk or bus further to school when there was a perfectly good building closer to their homes reserved for white people. That's segregation. Real estate agents preventing black people from buying near whites was called Blockbusting, and was different.