“Master” is the default branch and KiCad uses it for ongoing development, so it’s for the development version of KiCad. You can choose a tag for a specific version from the dropdown list instead of master (they are in the end of the list of branches).
On the other hand, you could install the libraries in the same way you installed the application. On Windows they are either bundled with the full installer or are a install time download option in the lite installer. On Linux they are distinct packages to be installed with the distro’s package manager.
If you decide to do this manually, you have to take care of certain things which otherwise are automatic and standard. As this thread shows.