Here’s the first line of those instructions:
These below instructions are for an installation of Home Assistant Core running in your own Docker environment
It clearly states you will be installing Core in a Docker environment. That means the core Home Assistant application (what you had when you installed it in python virtual environment) and nothing more. If you check Developer Tools > Info > System Health you will see that
installation_type indicates Home Assistant Container.
The installation process for the Supervised edition is more complex than the Container edition. It requires you install several prerequisites and then execute an installation script. The Community Guides section of this forum contains instructions for installing Supervised on several distros of Linux. However, the only one that is officially supported is Debian.