I don't know how much of a smoking gun this actually is, the evidence proffered doesn't establish anything - I can see some names there like Havilah Brooks or Celina Briar who are intentionally re-using the same title to create a series, for example. And this doesn't really get into the base rate of generic title re-use among encyclopedias. There isn't much reward for coming up with an imaginative title for kids, they're not very experienced. I'd have no trouble believing publishers come up with very similarly titled books in the kids encyclopedia all the time, they already recycle plots like there is no yesterday in fantasy.

I think the article's point is probably sound to some great extent, but I would believe I owned a book with a title like "100,000 Whys" when I was young. With a dinosaur and a rocket on the front. I loved dinosaurs and rockets, they're even still cool today.