At any rate, there doesn't appear to be anything too scandalous here. Some "brand entity" was curating content submissions, hosted on Medium. The curator decides to start hosting their own CMS site, and asks submitters for permission to re-publish submissions at the new place. Submitters obviously don't have to grant this opt-in if they don't want to. The end. ¯\_(ツ)_/¯
The only noteworthy item here is the sillyness of "brand entities" trying to use someone else's "platform" to bootstrap themselves. If you start off as a Facebook page, or YouTube channel, or whatever... it could be bumpy when you reach the scale of wanting to self-host your own site instead. That's the trade-off for having used that original host for its "foot traffic" benefits at the outset.
However, while Facebook/Reddit/etc makes sense for bootstrapping meme content, and YouTube makes sense for bootstrapping video content... for the life of me I cannot understand why anyone NEEDS Medium to get a print blog off the ground. It's PRINT, for goodness sake! The easiest and cheapest thing in the world to self-host. Does being on Medium really give you that much in the way of foot traffic or networking effect? I always find Medium posts by way of links from Hackers News or Reddit. I don't think I've ever gone to Medium simply to browse around and stumble across things.