Right above this in their docs, it says:
Requirements
* A server with Node.js 12 or newer
* A database (MySQL or Postgresql)
There is no assumption. Node comes with npm installed... Node is required to use this.
This can be any OS that has node, no one said anything about linux except you?
"OS" Packages is never mentioned, those are obviously node packages.
Everything must always be delivered in the native format of the OS software management subsystem; anything else is amateurism, not to mention a system administration AND a system engineering nightmare.
Why would I use Docker when I know how to make nice, clean OS packages?
For isolating your database from your host OS.