Perhaps because they have accents not associated as 'native' of that area. I moved away from my home country a long time ago: when I get back, people I don't kn

Perhaps because they have accents not associated as 'native' of that area. I moved away from my home country a long time ago: when I get back, people I don't know ask where I'm from because my accent has changed. After a few days it comes back and I blend back in. I believe this is very common to migrants, so not only do they have an accent not from 'here' but maybe they have a twinge of the local sound.