127.0.0.1 (aka localhost) isn't affected by your NAT setup. Your browser initiates this scan on the local loopback device, so the traffic will never even leave

127.0.0.1 (aka localhost) isn't affected by your NAT setup. Your browser initiates this scan on the local loopback device, so the traffic will never even leave your computer (even on linux, it's somewhat difficult to get it to route 127.0.0.1 to another computer and it'll break a lot of applications in the process or make them insecure). IPv6 with a public routed address still means there is a firewall, just like with NATv4. NATv4 just also has a NAT router with that firewall.