These laws, as you point out, are open to interpretation.
Discourse provides multiple options which forum administrators are free to use at their discretion as they see fit to enforce their own interpretation of the law.
We have multiple customers with GDPR deletion request integrations pointing at their site; some of them delete the posts & accounts outright, some anonymise. Some do it by hand.
But what they do is their decision - we aren’t the data owner of the forums - they are. And if they find our handling of anonymisation is insufficient (they have) then we address it (we did).
If you feel that anonymisation was insufficient on the site you’re talking about, it’s best to address it with them.