Answering the question "Which part of the world do you come form?" with "Western Hemisphere" would be considered odd by most native English speakers. If I was replying to a foreigner, I would more than likely answer the question by stating the country I come from. If I was asked by a fellow countryman, I would name the town I come from. In other words, "Part of the world" is an expression in English and shouldn't be taken literally.
I answer questions by giving as much detail as I think is relevant giving the context of the question. Giving more detail than is necessary would be considered strange by most people, but would unlikely merit any response other than in extreme situations where some smart ass might answer "Don't be such a nerd!". :) For example, if I asked a foreigner where they came from and they gave me their entire address in their home country, I would think to myself: "Eh... why did they state their entire address". However, I wouldn't respond by saying something like "Oh, what an exact answer!"