And since the article is using podman as an example: podman does have a manpage. The actual standard way of getting documentation on utilities, man podman, works just fine.
Put another way, I think `--help` is basically the CLI equivalent of generated API docs, whereas manpages are like long-form prose documentation. While you can get by with just one of them, the experience is going to be worse for certain use cases, and generally for anything beyond a certain level of complexity, your users will be better off if you provide both.