Hoi,
In them old days, this would be called a typical case of gigo or garbage in garbage out. It is hardly the only instance where what we define in Wikidata is not what we find in one of our sources.
It is to be expected, it is not something to get upset about.
At this time I am working on a division of the Netherlands that is largely wrong in Wikipedia. That is at most worthy of a blog post, telling people about it, making a list that makes this division understandable for use on any Wikipedia that wants it.
It is good to appreciate how erroneous Wikidata can be. It is good to appreciate that this happens with the best of intentions. The problem is not that there are errors, the problem is that we are lacking in well crafted workflows,build to help people fix what is wrong and report on it. We do not zoom in on known issues and therefore every item, every statement without a source is an issue. Even worse, many sourced statements are questionable but we have no way of classifying sources. Everything is a potential problem and we do not contain errors and have people work on what we know may be wrong.
That is an issue worth talking about.. The rest is just a drop in the ocean.