U.S. cities, maybe. But get gather natives from the rural parts of any state and you'll find a ton of cultural variation. Saying rural Louisiana and rural Oregon are culturally homogeneous is just wrong. Sure, we all speak one language, but so do France and half of eastern Canada.
What? If they're both from major cities in the two states, they have way, way more in common than a Belgian and a Slovenian in the same room.
A Serbian and a Portuguese are much farther apart ( language, cuisine, history ( even if there are some small parallels like both being occupied by a foreign neighbouring power, independence being won by blood, and an oppressive regime in recent history, Ottoman occupied Serbia , world wars, Yugoslavia couldn't be farther from seafaring trade and colonialism Portugal).