1) They could be using café wireless from different cafés that are backhauled to the same data center (or LinkNYC as another commenter mentions.) 2) They could

1) They could be using café wireless from different cafés that are backhauled to the same data center (or LinkNYC as another commenter mentions.) 2) They could be using residential IPs, which are frequently reassigned. When my router restarts, I usually get a new IP address from the ISP's pool. This is more common for some ISPs and locations than for others; at my last place, we had the same IP address for 5 years. 3) Carrier-grade NAT, also mentioned here.