Worse still, it starts by assuming runlevels still have a meaning. Nearly all modern distro's are now running systemd, which has no notion of runlevels (targets are kind of the same but also very different!)
The newest distros use systemd, but IT departments seldom run the newest distros on servers. For example, AWS's Linux AWI still doesn't have systemd support.
In several cases, the versions that preceded them ran upstart. Advice that has a blanket assumption of the presence of van Smoorenburg init has been wrong for longer than systemd has been around.