There is little difference between Guix and the Guix system when looking a little more closely. Even when using Guix as a package manager it won't link with any of your OS libraries, so you end up downloading or building variants of libraries that you may already have on your host operating system --- that's by design as it unlocks reproducible builds.
The scheme you have now is confusing for no reason. I saw this news on Phoronix and even after reading the article I couldn't tell if it was the pkg manager or the distro that had reached 1.0 (I guess it's both?).
I understand what you mean by the difference. (I currently overlay Nix on top of a different Linux distribution.) But without the "system" part, Guix on its own is still not strictly an OS, since there's no kernel being deployed. A pedantic point, but an accurate one I think. :)