I am very unfamiliar with the protocol, but my impression from a little reading is that the sharing computer broadcasts and the receiver listens. This appears to be for some CUPS specific browsing/discovery protocol rather than mDNS/DNS-SD (cups-browsed supports adding printers discovered that way but depends on avahi to handle the mDNS part).
Isn't listening on 0.0.0.0 instead of localhost only needed if the machine itself is hosting a printer that needs to be accessible to other hosts?