There are quite a few people whose own world is very small or limited in exposure to the rest of humanity. These ones make assumptions due to a lack of a more broad understanding of the real world. They are judgmental and try to categorize you. They are surprised when they learn more about you because you don't fit the mold they have already established in their mind. They are ignorant of anything that isn't part of their own world. It's a classic case of judging the book by its cover.