Medium is bullying the curators it courted

1) I publish an article on Medium

2) Hacker Noon requests that my article be included in their 'publication' on Medium. There is an understanding via Medium about what this means (ie. that I own my article and can post it to other publications as well.) I accept Hacker Noon's request. I benefit because Hacker Noon puts my article in front of more eyeballs.

3) Hacker Noon decides they want to leave Medium. They send an email to contributors asking them to sign a new terms of service.

4) Medium emails the contributors and says: Let us clear up some confusion; Hacker Noon has no rights to your content unless you grant it to them.

Why is Medium the bad guy here?