Nebula used to not have a discovery feed and just a most recent videos one, so I could see someone wanting to filter out creators who they've watched and decided aren't for them to have a better chance of potentially finding new channels they do want to watch.

EDIT: Also, not sure if you're just joking or not, but I'd bet the author is a Mike Boyd fan. I feel like people tend to use examples of things they like in documentation, and it's just an example.