1) Streets in New York are closed all the time for anything and everything. There are street fairs/farmers markets that randomly shut down 10-blocks at a time. The MET Gala shuts down blocks. Parades shut down 30 blocks at a time.
2) A street being shut down usually means for cars, not people.
3) Madison Square Garden and Yankee Stadium are rented out by rich people for private events all the time.
4) Holiday weekends like July 4th are even quieter here than other times because people leave to go to beaches, upstate New York, friends and family, etc.