Why isn't deriver and realize identity functions (see example)

I am seeing this weird issue that confuses me.
Basically realizing a derivation gives a store output.
Asking for the deriver for that derivation doesn’t return the same derivation.

huh?

❯ nix-store --realize /nix/store/cizs4p15n8m10amjppslimb71s2c6vg0-ruby-3.1.5.drv 
warning: you did not specify '--add-root'; the result might be removed by the garbage collector
/nix/store/c4bdx4dja3h06xg1ksv3f51alp5a44li-ruby-3.1.5
/nix/store/q5gsd06fvsx43liny95w2jmh32cf3w4y-ruby-3.1.5-devdoc

❯ nix-store --query --deriver /nix/store/c4bdx4dja3h06xg1ksv3f51alp5a44li-ruby-3.1.5
/nix/store/qka91zsrlrah0cf0z6q9dqqk1imvcypa-ruby-3.1.5.drv

Ruby is not a fixed output derivation so I have no clue what’s going on.
(I read fixed output derivations could have multiple derivers)