I really didn't take that as their implication. Apartments in New York are often not that comfortable--they can be cramped and cluttered, and not even all that private thanks to thin walls and sometimes even shared bathrooms. So even an introvert with that kind of apartment tends not to spend much time in it apart from sleeping. Instead they'll go to libraries or museums or parks or makerspaces or cafes. It's surprisingly easy to be alone in public in New York.

I think that's all they meant. I see how you could take their comment differently, but I think they were being sincere. Actually spending a lot of time in their tiny dismal one-room apartment with no natural light is actually a mistake that some introverts make when they first move to New York, and it's genuinely depressing to do that.

A caveat to all this is that I've only spent very brief periods in New York, and I do find it overwhelming, partly for this reason. But yeah. I don't think that person meant to condemn spending time alone; they were just saying that treating a New York apartment like a solitary confinement cell isn't good for your mental health regardless of your socialization tendencies.