If a show has a public and open feed that you can subscribe to with gPodder, AntennaPod, Thunderbird, old Firefox versions, whatever, it's a #podcast.

If this public and open feed doesn't exist, or is kept undiscoverable so that it might as well not exist, it's not a podcast.

It really is that simple. Put a friggin #RSS or #Atom feed on there with an enclosure element, that's it, that's the definition. That's the podcast.