What the author describes as being around people actually sounds like social isolation: yes, NYC is full of people but the way the author describes it, they're

What the author describes as being around people actually sounds like social isolation: yes, NYC is full of people but the way the author describes it, they're all strangers. This isn't alienating, this is alienated. Humans have evolved to live in small to moderately sized groups with close relationships and shared activities across the group like communal child rearing, food procurement, games and rituals. This also hinges on being able to make an impact on your surroundings and maintaining use-based ownership. Contrast this with living in a megacity: outside your (rented) apartment the closest thing you get to ownership is public property which effectively is owned by noone while all private property is owned by someone else who is most likely a faceless corporation or a complete stranger to you. You are constantly surrounded by people but you don't know any of them and most people you will likely encounter too infrequently to form any lasting relationships with. They're all strangers or outsiders with goals at best irrelevant and at worst contrary to your own but they're also similarly isolated from each other so they don't even form a "foreign tribe" you can try to assimilate into - apart from a vague notion of "acting like you belong" by following the shallow social norms. What the author describes as solitude on the other hand is the individualistic rebellion against this: carving out "your own" space in one that is unclaimed (or at least not inhabited and actively guarded against your temporary use of it). The interaction he describes is a lot more intimate - not because he was nude but because he was interacting with discrete people, not faceless members of a crowd. Of course as others have pointed out this isn't lasting and "actual solitude" is a very different beast and can be equally harmful and alienating. So the answer is a collectivist rebellion: finding a "tribe", looking for peer groups to form closer bonds with over shared interests or experiences. Often this is what motivates people to move into suburbia where they of course often still experience the same isolation as everyone retreats into their family home due to the lack of horizontally organized communal spaces.