I would have known that neodymium is some kind of a substance, but I wouldn't have known or remembered that it was an element without checking. I'd probably answer I knew the word "degauss" but if I had to explain what it physically is, I'd struggle. I might not remember what distinguishes howitzers from other artillery pieces. Out of these, I'd probably report not knowing neodymium, knowing howitzer, and be a bit torn on degaussing.
Someone might know that a katana is a weapon, or "some kind of a ninja thing", or maybe even a sword, but might not feel comfortable enough about the details to report knowing it. Also, it might be more well-known among younger people who know the pop culture than people who don't.
But then, I guess it might also be that people just have rather different areas of familiarity, as the article indicates, and a significant part of the English speaking population might be as clueless about katanas as I am about tulles, or whatever the plural for that is. I only knew one or two of the words from the upper half. I'm not a native English speaker, though, which perhaps not only limits my vocabulary compared to native speakers but might also tilt things even further towards the science/tech words.