Everybody, STOP and think!
This NOT a race issue the OP is mistaken in her perception.
It is a NYC vs the rest of America issue.
As many NYers may have experienced when visiting or living in the rest of America, especially the south and midwest, people greet each other on the street.
In NYC, people do NOT greet each other, often when people do, they are seen as strange, even threatening.
In most other places in America, when you come upon a stranger on the street, you and the stranger will greet each other with a 'Hello', Howyadoin' or some such gretting; AND many times strangers upon greeting will, indeed, stop and chit chat.
Being a born and bred NYer, the first time I left NYC and experienced this I was a bit taken aback, but quickly got used to it and came to appreciate it MUCH! After having lived in the south for awhile, returning to NYC, it took awhile to regain the naturally rude demeanor.
I believe the OP, not being a NYer, acted with the common manners she was accustomed to, greeting people she came upon on the street.
The race thing probably comes into play, because she was white, and in a minority area, blacks saw her as nonthreatening, and so returned her greeting, and may have stopped to chat with the crazy white lady. This is even more likely if she came upon older blacks who are closer to their southern roots.
In contrast, whites are more likely to view her behavior and approach strange and possibly threatening, and acted with a NYers customary rudeness, in other word she was simply ignored.
This is quite likely, given that the neighborhoods she visited were generally minority areas, and the whites walking the streets there are likely not residents, there for business/work and are likely 'on guard', as a natural state when traversing a minority area.
Strange white lady with the friendly greeting is probably setting them up to be robbed. This is what a white NYer in that situation might think. The natural reaction is to put your head down and keep moving.
Make sense?
So, lets not go all racially ballistic!