It's more likely that both are derived from ColorADD, but the idea is also simple enough, conceptually, that they all could have thought of it independently.

Getting it wrong: Red should be the Chevron as a metaphor for fire, Yellow should be Circle as a metaphor for Sun, Blue should be line as a metaphor for the sky + horizon.

The problem with requiring that your symbols are metaphors for things is that those things may not relate to the context in which you are using the symbols. At which point it just adds confusion to say that the yellow symbol represents the sun.

Additionally, people are never going to agree on what should represent what, as you yourself demonstrate; the author explicitly rejects that the blue symbol should be the metaphor for sky, yet for you it apparently felt like the best choice:

For blue, there are two obvious choices. The sky and the water. Water makes a more practical choice since the sky is inherently formless, and therefore quite difficult to represent symbolically.