When I visited New York City (and the US) for the first time in like 2010 I was taken a back but how much Americans like to chat randomly so this is strange to read.
I remember a random guy was chatting to me in the subway, then I got out, waiting at a crosswalk for the green, in those 15 seconds another guy starts another random conversation. In the first 2 hours of the trip I already had maybe 10 random circumstantial conversations. The whole trip I felt like if I wanted I could always be talking!
This was my experience too. The USA is the only country I've ever been to where random strangers will strike up a conversation with me completely out of the blue, and I've travelled quite a lot.
It's both regional and depends on how you are perceived.
I'm an introvert and I'm always surprised when a stranger talks to me, no matter where I am. But I make a point of always being pleasant back, no matter how I feel about it at the moment.
Sometimes it's just a couple sentences, and sometimes it's more of a conversation. It'd probably be more if I was better at conversations.
The only exception is if I feel the other person wants something from me, or they seem crazy or dangerous. I don't engage with those types.
NYC is very different in that regard from most anywhere else in the US. Random people tend to talk to each other. There’s a vague sense of “we’re all in this shit together”. Maybe it’s something to do with living on a cramped island, with no choice but to work together.
For people whose cultures value reserve and privacy, visiting the U.S. is a study in cross-cultural dynamics and sometimes a serious test of social boundaries. Your comment reflects that. The loudness, friendliness, warmth, and (occasional) casual intrusiveness is both a reality and a stereotype. It always reminds me of this hilarious Harry & Paul (UK) sketch: https://www.youtube.com/watch?v=BGc3zFOFI-s