(First, super excited about this project -- I'd really like to see how container compares to docker with one of my containerized apps.)
When you run container-compose up -f <foo> if there's a docker-compose.yml file present, it defaults to that rather than using the file passed via the -f argument.
It looks to me (as a novice, so I could be quite wrong) that the check on lines 85-90 of ComposeUp.swift finds one of the known files and then sets the filename before it then reads the path provided.