Came here to make sure that Art of problem-solving and beast Academy are mentioned. They are fantastic. My son is deep into art of problem-solving after having finished beast Academy.
I think the second mocks the inclination of humans to reflexively admire everything that high status (ie rich) people do or say. It is similar to this amusing Yiddish saying: https://www.yiddishwit.com/gallery/sing.html
I have been looking at trees my entire life, and never thought to even think about this “plumbing” ratio. What a lovely example of how Leonardo combined mathematics and observations.