Yes, but exactly that was/is the issue of this bug. cups-browsed was attaching itself to every available IP on the system. And cups-browsed can’t only be bind to localhost, it would defeat the whole purpose of that tool. For it to be able to find other printers in the network it needs to be bound to a non-localhost-IP address. So, not much to sandbox
Unfortunately many of the routers provided by ISPs I have seen where not configured that way by default. They only used NAT as firewall, so without configured port forwarding nothing could be reached with IPv4. But for IPv6: If you know the IPv6 for any system on the local network it is free available on all ports. It is the first thing I check when someone asks me to check their network or configure their internet, and only Fritz!Box have a sane default for IPv6 (but to be honest my other experiences are mostly with shitty Vodafone and german Telekom routers so it is a very limited set, and I really hope that most others are better.)