The similarity is definitely on purpose. It pulls ideals from both nixpkgs as well as the cloud native buildpacks.

Our goal is to make reproducibility more approachable/less cumbersome, and for people to be able to define additional nix/apt/etc packages added to the container .

You can add package you'd like via the environment variables NIXPACKS_PKGS (or NIXPACKS_APT_PKGS for apt)