Correct, but you can’t reply or vote there without an account on beehaw or another instance that they do federate with. That’s what they are concerned about. They are saying they are concerned about just anybody making posts or comments on beehaw because of open user registrations on lemmy.world and sh.itjust.works.
Those are outdated posts. See https://lemmy.world/post/149743 for explanation.
For companies, GDPR applies to people in European Economic Area whose data is used by companies, or companies that have an office in EEA or another stable arrangement in EEA and process personal data of people located anywhere.