That's what I was thinking. The only reason that I thought Nix on FreeBSD as even remotely possessive is that, as I remember things, it's possible to run the Nix package manager on non-Nix systems.
You can run nix-the-package-manager on FreeBSD, so you can build stuff. However I think it would take a lot of novel and elegant boilerplate to have nix manage network config on a BSD system.
NixOS is a Linux distribution managed by nix-the-package-manager.
