Socializing in a Small town Versus a Big City

It’s always obvious when a friend from a small town comes to visit the big city. My friend from back home greets literally everyone he passes, which—as a city local—honestly makes me a little self-conscious.
For instance, if he sees a dog he likes, he’ll stop the owner right on the sidewalk. He’ll blurt out, "I miss my dog so much, I just have to pet yours!" and dive right in for a scrub. Meanwhile, I’m just standing there awkwardly, caught in the interaction whether I have somewhere to be or not.
The neighborly vibes are just as different. Back in his small town, his neighbor’s smoke alarm started chirping for a new battery while they were away on vacation. He didn’t think twice—he just went over and fixed it to solve the problem. In the city, most of us don't even know our neighbors' names. We wouldn't dream of stopping them for a quick "hello," let alone entering their home. We basically live in fear of ever actually needing anything from the people living right next door.
Maybe this dynamic applies to any "town vs. city" comparison, but since these are the only two worlds I’ve lived in, the contrast feels pretty stark.