It’s a normal Dutch last name.
Also, the naming of the holdings is the same. So they probably registered it at the same time. Anyway, information can always be checked at the chamber of commerce
It costs 2.50 to check the names of the owners of these companies at the chamber of commerce if that makes you doubt whether or not it's actually the name. This means that the owners were effectively outed by the publication anyway.
Not really, the point of Dutch privacy law (and similar EU laws) in this context is not to deter a dedicated investigator, but to merely put enough of a hurdle in place that everyone reading the article won't see the names of suspects, and they won't show up in web searches etc.
Iirc it's not even an actual law, more of an agreement between all news organizations to not publish names like that. I seem to recall Geenstijl(Dutch "news" site) publishing full names and not getting in trouble over it.
If the bar for being a "dedicated investigator" is copy-pasting a string and paying 2.50, I think we just have different views on this. Your views about the intent of specific laws aren't relevant, as there are AFAIK no laws about news publications that apply to what we are talking about.
Not mentioning lastnames is only a convention by journalists and the media. Publishing lastnames in the media is not a violation of the law. News website geenstijl.nl regularly publishes full names of suspects or criminals.
The convention already existed before the internet.