1. Your printer probably puts a secret code into everything you print (not just money-like things) with the time and a serial number of the printer. [0]
2. Windows and MacOS constantly sends the serial-numbers of your connected devices back to the mothership. [1][2]
3. So when you print out a flyer that somehow annoys the regime, they read out the serial number, then call a buddy at Microsoft/Apple.
4. Now there are thugs knocking at your door to talk about how your picture was criminally mean to Dear Leader.
[0] https://www.eff.org/pages/list-printers-which-do-or-do-not-d...
Also, the home page of that "blog" points to a 404 not found, and the footer of the blog says: "Official blog of NetworkMonitor — network monitoring and macOS privacy insights." and I can't seem to find any application made for the Mac called "NetworkMonitor".
Originally the comment was Windows/Microsoft-centric, and then I thought I'd better broaden it so that nobody makes the mistake of thinking Apple is significantly safer.