There is no compelling evidence proving that the disease cannot spike in NYC.
There are small hints that it MIGHT not be possible. The antibody tests measured the infection rate around April 15 or so, the number should be higher now. Second, there is some evidence that a percentage of people don't develop antibodies (only T cells) but are immune. Finally, we don't really know what is required for herd immunity.
None of this is to say you are wrong, just why it MIGHT be possible that NYC cannot have a second spike.