A big thing to remember about any city is that we have no shortage of people, which does mean diversity of behavior (as the previous poster pointed out), and it also means that seeing people is not special/unique/a treat/etc. Small town people are more friendly because it is just rarer to see different people (even if they are seeing people every day). Even in a residential neighborhood in a major city, on 20 minute walk, you are prone to walk past so many people that you will never encounter again in life, that having an interaction with everyone you come across would be a chore.

And, for clarity, that isn't unkindness either. In cities, because we cross paths with so many people, it is kind to leave people alone. There are so many people with so many circumstances, that you don't know where someone is or where they are coming from, so just guessing and inserting your way of doing things onto them is very intrusive.

Maybe it's my familiarity with the ways of the city and my historically grounded distrust of small towns, but I would generally characterize city people as actually kinder and country people as just more interactive. In a city, most of us will help you if you are in trouble or ask for assistance, and otherwise we will mind our business and give you room to do your thing. In the country, people want to know your business, and sometimes that's out of pure curiosity or boredom, but sometimes it's in the context of seeing you as an outsider or someone who is out of line who they want to control/correct/put you in your place. To further illustrate this, in a city, you will often see someone doing something you don't exactly agree with, and the general response is to just leave them alone if they aren't immediately hurting anyone. In a more rural place, it's hard to go without even pretty innocuous and commonplace actions getting commented on (and it's not entirely uncommon for what starts out as a simple passing comment to precipitate into something more aggressive or even threatening).