The page, https://www.funtoo.org/Linux_Fundamentals,_Part_1 says:
Welcome to "Linux fundamentals," the first of four tutorials designed to prepare you for the Linux Professional Institute's 101 exam.
Linux Professional Institute? That's new to me. Quora user, Pieter de Bruin, Cloud Support Engineer at Amazon Web Services (2016-present), answers to the question: https://www.quora.com/Which-Linux-certification-is-better-Linux-Foundation-or-LPIC
I don’t think the other answers on this thread is accurate or at least up to date. The Linux Foundation’s certifications are performance based which is the most real world relevance that a technical certification can get.
They may be new but are in my opinion far superior to multiple choice or any (Brain Dump) guaranteed pass certificates such as LPIC. In order to pass the LFCS, or LFCE exams of the Linux Foundation you need to have exercised setting up the relevant services or other challenges posed by the exams multiple times in order to just finish in time. Unlike the RHEL certifications they are distribution centric so you can choose to do your exam on CentOS, Ubuntu, or Open Suse.
The Linux Foundation is also a non-profit who hosts the Linux Project, employs the Linux Founder (Linus Torvalds) and release the kernel updates that are implemented by all the distributions.
If you are passionate about Open Source technologies I do not see more relevant source to support when it comes to getting certified.
I'm not asking whether your Linux Fundamentals guide is suitable for The Linux Foundation's exam or certificate. I ask why do you favor to mention Linux Professional Institute and not The Linux Foundation in your learning resource. Perhaps, when that guide was originally written, only Linux Professional Institute was around, and not yet The Linux Foundation? Or you may have other reasons.