Why was my HP printer automatically shared on my WiFi?

I got a pleasant, but odd surprise today. I went through the whole rigmarole of installing HPLIP on one of my laptops, finally getting an ENVY 5644 working with duplex, colour and everything. Having a number of laptops at home, I dreaded having to go through this again and again, but lo and behold, I didn't need to! For some reason, the printer was automatically shared to the other machines! Granted, I like to keep my computers as a tightly knit family (passwordless ssh, filesharing via sshfs for example), but this printer sharing was utterly unexpected! I have NOT flagged the printer as shared, thus the surprise.

Anyone here with an idea as to why I got this lovely surprise today? (All machines running Ubuntu 21.04 BTW...)

CUPS is using the Internet Printing Protocol https://en.wikipedia.org/wiki/CUPS

When one computer is set up for a printer, other computers connected to the same common network can do print jobs. I.e. if the "printer computer" is running.

Info, "How to share a printer between multiple computers" https://www.computerhope.com/issues/ch000710.htm