Whether or not this info should be in acoustics books or theory books is not relevant to the new learner, that's where it is! I actually think a crash course in acoustics would be a good addition to a comprehensive theory book, but it doesn't change the fact that no theory course or book has this stuff (not even my pitch set texts!)
I teach music students regularly. I spend a lot of time explaining what something is called in various contexts. They need to know this to learn in a productive and not frustrating manner. They can then learn later why the terms are imperfect and used differently in different subcultures.
But no argument on that is going to convince me that it's good pedagogy to tell new readers that a post on acoustics and synthesis is on music theory. That's just counterproductive at best, or ignorant at worst.