Why this prejudice?

Some days ago a man came to our office to buy an apartment from a particular project. He wanted to know whether any buyer from Barisal was there. According to him, it is impossible to live with a neighbour from Barisal. My other two co-directors smiled silently as I am a man from Barisal. Over two decades ago, I along with my wife went to the house of one of my acquaintances. There were a dozen people who were engaged in a debate over “who are the worst people in Bangladesh?” The conclusion of the debate was that the people of Comilla, Noakhali & Barisal were the worst! My wife also fell into this category as she is from Noakhali.
Interestingly, the buyer whom I have mentioned at the beginning of this letter is also a man from Comilla. I think many people have positive or negative ideas about people of some particular districts or areas. But can an area produce good or bad people? As our country is very small, the geographical impact cannot be a big one to change the mentality of people to a great extent. But many people have such strong prejudices.