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).

EDIT: Here's a description of the protocol in question: https://opensource.apple.com/source/cups/cups-327/cups/doc/h...