Not necessarily: nix the package manager runs fine on other distros, as well as FreeBSD, OSX, Windows, SmartOS, ... Nix doesn't need fancy filesystem shenaniga

Not necessarily: nix the package manager runs fine on other distros, as well as FreeBSD, OSX, Windows, SmartOS, ... Nix doesn't need fancy filesystem shenanigans to do its job: build isolated packages with complete runtime dependencies. NixOS is built on top of it to provide atomic system-wide upgrades and rollbacks.