Why does github:sodiboo/niri-flake exist?

I'm a relatively new user and I've successfully set up Hyprland with home manager. I wanted to try out Niri though but it's a bit more confusing for me. What's the point of that repo? Does the Niri that's in nixpkgs not work with home manager? Is that repo, and that repo alone, expected if you're using home manager and want to manage Niri with it?

Thanks!