The Waldo zk proof isn't a good example. You can easily fake knowing where Waldo is by gluing a Waldo to the board you use to hide the book. That way you can even proof you know a solution for a picture that doesn't even have Waldo in it.
This can easily be remedied by having the verifier ensure the prover is in an empty room, equipped with only cardboard and scissors.
It's a perfectly fine example! It doesn't have to be academically rigorous, it just has to demonstrate the basic idea of proving a thing without exposing the thing. Yes, obviously it's not actually a formal ZKP, but analogies are imperfect.