I was confused also but I think what is being said here is that "noon" is de-coupled from "12:00" and becomes relative to the local position of the sun. So if you are at UTC-4 today your "noon" would happen at at 8:00 and if you were at UTC+2 your "noon" would happen at 14:00.
Honestly I had a hard time even figuring that much out. Time is hard.
This reminds me of a discussion about NFTs recently. I caught myself having an opinion without really knowing how they work. So I googled it and only found vague descriptions. Then I looked for an actual ETH blockchain contract that implements NFTs on Github [1], read it, and it was all very simple and clear. (So for me it was "How to Learn complex Things Quickly by realizing they are not that complex at all.")
So in some cases I'd put "Read the Source Code" at the top.
Code is not quite mathematical notation, but it is a concise way to express something..
Honestly I had a hard time even figuring that much out. Time is hard.