Mr van Asselt was a prominent professor at the Utrecht University. He is one of many professors known to Wikipedia. Given that I regularly harvest data from categories, it makes sense for me to use the English Wikipedia as it has an article about Mr van Asselt.
The equivalent category on the Dutch Wikipedia knows about more faculty members and then there are categories in several other languages as well. All of them may know about even more faculty members.
As we aim to share the "sum of all available knowledge" with our readers, Mr van Asselt is a timely reminder to the audience of the Dutch Wikimedia conference that no Wikipedia does know it all.