[1una]

In this specific case, nix uses fetchFromGitHub to download the source archive, which are generated by GitHub for the specified revision[1]. Arch seems to just download the tarball from the releases page[2].

[1]: https://github.com/NixOS/nixpkgs/blob/3c2fdd0a4e6396fc310a6e...

[2]: https://gitlab.archlinux.org/archlinux/packaging/packages/ib...