Cool idea, horrible dataset. Its limited to things in Wikidata rather than using OSM, and it must have an article on Wikipedia in English to count so I am sure it is missing just based on that. And somehow it misses many castles (and other categories it includes) which do meet those requirements.

There is no definition of what they use to categorize anything either. And it clearly isn't applied consistently. There is a Château category and yet many things with Château in their name are tagged as castles.