Person from the US here. When I am on a trip, I don't like being asked where I am from if only because it happens so often. After you have been asked "Where you folks from" ten or twenty times, the question gets old.
I particularly don't like it when the encounter is casual, for example, when it is part of the "greeting" at a restaurant. If we have struck up a conversation with someone (about archaologicalarchaeological sites, or the best route to X, or sightings of a cougar near the trail), the question is a natural one after awhile.
Moreover, I genuinely don't know how to answer the question. "Where you folks from?" Does this mean
Where were you born?
Where did you grow up?
Where did you go to school?
Where are you currently living?
Where do you feel most at home?
Only the third and fifth questions have any potential to lead to an exchange of views. The other three have only trivial answers.
So, yes, from the perspective of this middle-class, Virginia born, New England brought-up, MIT alum, Virginia resident, and lover of the Sierra above timber line, "Where ya from" is not only a rude, but a boring question.
That being said, in a foreign country where I am by definition a guest, I would not be offended by questions I would consider rude in my own country.
Edit in response to comments: In my culture -- and in my opinion -- asking personal questions of total strangers is rude. Asking a total stranger "where are you folks from" is a personal question, not a conversation starter.
It is not in the same class as "How are you?" That question is always supposed to be answered by "Fine, and you?" You can be terminally ill, and you will still say "Fine." No stranger or casual acqauintanceacquaintance wants to know how you really are.
But if I were in a foreign country, I would accept that I do not understand the customs, that I am a guest, that in my monumental ignorance I probably do things that are impolite by their standards, and I would take offense at practically nothing.