No semantics. AC 91-57 is the operating authority for hobbyists. But that does not change the nature of what an AC is. It is, by definition, an advisory. The real point of the document you linked to is that commercial, non-hobbyist operation are held to a higher standard. And you cannot slip under the radar by pretending to be a hobbyist.

Notice that the AC also mentions choosing an operating location away from "parks, schools, hospitals, and churches." Which if you want to be as technical as you are being that no more park flying, or flying at schools.

But the key is to focus on the FIRST sentence of the AC:

"This advisory circular outlines, and encourages, voluntary compliance with, safety standards for model aircraft".

Again, there is no force of law, despite the latest document noting that the AC is the operating authority for models.