I now live in a neighborhood that is more mixed, both economically and racially. I know many of my neighbors, and talk to them quite often. We have four parks within walking distance, and a community garden within one of them. We have sidewalks that are heavily trafficked, and most houses have front porches. Once a year, there is a neighborhood music festival, where people play music on their porch, or in their driveway. I'm sure that many good people lived in the neighborhood I lived in previously. However, it wasn't the kind of environment that encouraged interaction. On a community level, I act differently in my current neighborhood compared to how I did in my previous one.
Yes, I think the economic situation the author talked about was, largely, a red herring. Community design matters a lot. If the place you live requires you to drive your SUV through a guarded gate into your enclave of detached houses, you're probably not going to be spending much time hanging out with your neighbors. Instead you're going to go inside, lock your doors, and wait until the guards indicate it's safe to leave the enclave again. On the other hand, if you're in a neighborhood where apartments, shops, offices, parks, bars, and restaurants are all mixed together and you can walk everywhere, you're probably going to be seeing quite a bit of your neighbors, and probably even enjoying it. The U.S. has a lot of very isolating community design, with miles and miles of housing in its bedroom communities, then, a dozen miles away, miles of office parks, then a dozen miles away, miles of shopping districts, and so on. You have to spend a huge chunk of your life stuck in a car just to get from where you work to where you eat to where you shop to where you sleep.