It has been mentioned in one of the pull request that this guide was being discussed on HN right after it got here: https://github.com/imthenachoman/How-To-Secure-A-Linux-Serve....
There are two fresh threads on Reddit:
https://www.reddit.com/r/linuxadmin/comments/arx7xo/howtosec...
https://www.reddit.com/r/linux/comments/arx7st/howtosecureal...