Fair enough; it’d depend on how you got your hands on nixos-option then. If you used nix-shell rather than the one installed by default you might see this behavior, because it’d refer to your root channels, which may or may not be up-to-date depending on how you deployed your flake.
If not, no clue, I haven’t verified myself that the nixos-option on current nixos-unstable works, fwiw.