The fingerprint method is named Canvas Fingerprint. It uses the canvas component to build a fingerprint of your PC. By adding random noise to the canvas the canvas is altered slightly by the browsers anti tracking feature and the detection does not work. I don't know how the canvas fingerprint itself works.

If I had to guess, there are various fingerprinting techniques, and some of them use things like drawing on canvases to track you. They are probably referring to that.

Best practice is to have a second browser or profile for specific sites that require you to disable fingerprint protections.

Source: https://github.com/arkenfox/user.js/wiki/3.3-Overrides-%5BTo-RFP-or-Not%5D

I had similar issues with canvas fingerprint prevention, the noise added to the canvas messed with photo uploads on sites that gave you a little editor. That used canvas I assume and all my uploaded pictures would end up tinted various shades of green/purple I think. So I had to just not use that setting.