You are not at all overreacting! I am glad that you are able to speak about it in such a passive way, I would have slapped that gentleman who was selling flats. I myself have experienced that wuality of life in Delhi is better and less prejudiced as compared to Mumbai. There we have seen so many maharastrian societies who don't want Gujjus, biharis, Upiites, muslims amidst them. The vegetarians would make a major fuss about even an egg being bought in the neighbourhood(all though they would kick and stone stray dogs and cats brutally). They even have prejudice on songs bieng played for community gatherings, and would only invite their own communities for most society functions!! I suggest you let them know of what you think of them everytime you face such situation.
