"The inside of the network stay anonymous" sounds like they are talking about internet access to the internal network.

So OP is correct, it does apply a measure of security. Port scanning someone behind NAT isn't possible, you just end up port scanning their crappy NAT router provided by their ISP unless they have specifically opened up some ports and directed them to their internal IP address.

You end up just port scanning their crappy router on IPv6 as well because ports that are not opened are stuck at the firewall either way, no matter if you use IPv4 or IPv6.

Just because every device gets a public IP does not mean that IP is publicly accessible.

An advantage that IPv6 has against port scanning is the absurdly large network sizes. For example, my ISP gives me a /56 prefix, that is 4,722,366,482,869,645,213,696 IPv6 addresses. Good luck finding the used ones with the port open you need.

Even with just a /64 prefix you get 18,446,744,073,709,551,616 addresses, way outside the feasibility of port scanning.

Compare this to IPV6 where you get a slice of the public address space to place your devices in and they are all directly addressable. In that case your crappy ISP router also is a “proper” firewall. Strangely enough it usually is a “stateful” firewall with default deny-all rules that tracks network connections and looks and performs almost exactly like the NAT version, just without address translation.

realistically, it wouldnt surprise me if ISPs started NATing on residential IPV6 networks, just for the simplicity, but still allowed end users to assign their own IPs if they so pleased. Given the surge in shitty IOT devices, that's probably a good thing for most people. Though a firewall would also accomplish this as well.