Level 88
If you downloaded Homestead by cloning it in some directory you can see the version in that directory by simply typing git status. It will show what branch/tag/commit you are on.
So Homestead itself is a project with configurations and so on and has nothing to do with the version of the vagrant box itself. There can be new configurations or setup methods for new users without changing the box itself.
The number 6.0.0 is the settler project in the laravel namespace on Github. This is the version number of the vagrant box. This is the script that builds the environment in the vagrant box for Laravel: https://github.com/laravel/settler/releases