Pretty sure that's because podman-compose literally calls docker-compose under the hood.

e: from the manpage:

"podman compose is a thin wrapper around an external compose provider such as docker-compose or podman-compose. This means that podman compose is executing another tool that implements the compose functionality but sets up the environment in a way to let the compose provider communicate transparently with the local Podman socket. The specified options as well as the command and argument are passed directly to the compose provider."