[ffk]

Docker save (and presumably podman too) adds that metadata as a file in a tar. Each layer becomes a tar that is nested in the top level tar.

[hutrdvnj]

A container registry allows you to download multiple layer simultaneously and only those that you need (that you don't have in cache).

[e12e]

Indeed, registries don't do much more than what:

    docker image save foo:latest \
      | ssh pod docker image load

does (the stream is a docker tar archive with layers and metadata).