The Wikidata software is extensions to Mediawiki (which is maintained by WMF), and though the extensions are primarily developed by a Wikimedia chapter (Wikimedia Deutschland), it's disingenuous to say that Wikidata is fully maintained by them. Its operations, at the very least, are maintained by WMF, and quite a bit of development and a large amount of code review was done by WMF.
Similarly, the test/dev for Wikidata is part of Wikimedia Cloud services (which I created). That environment is also WMF run.
Can you cite any evidence (even in German)? The only thing I'm sure that was done by WMDE is about Wikivoyage (which is definitely more complicated than it seems, mainly because the English version was a fork of WikiTravel).