He seems to be pissed off that Red Hat discontinued the free CentOS distribution. And instead of paying for Red Hat, it goes to Rocky Linux, a free fork of Red Hat, just like CentOS. It is fine (at least legally), but the paid Red Hat distribution is no less open-source than Rocky Linux, in fact, the latter exists because Red Hat is open-source.
That's why I think this article particularly ironic, it says that Red Hat is not "true" open-source and then made a move that is only possible because Red Hat is open-source. It didn't even go to something like Debian, which is the most "free/libre/open-source" of the major distros, it went to the clone of the distro they criticize.