Once we get to this point of making a guess, then deciding that it's probably right because of some other guess based on any data that might be willing to fit the guess, I agree that the warning about not saying those are facts is most welcome.
All I could find about brain "rhythm":
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3553572/ No sign of one frequency to rule them all.
From somewhere else:
And the one thing I could find that's a miss but almost could fit with a lot of imagination and cherry-picking:
https://www.science.org/doi/10.1126/sciadv.aao3842 where they suggest that they manage to synchronize to the envelope of sound and only up to about 5Hz.
I have no idea if that is true. The visual cortex is the biggest area of the brain strictly dedicated to one of our senses, and all the research I have seen seems to involve more areas of the brain with sound only when speech is involved. With elaborated speech in a song referring to many things and maybe various activities and other senses, maybe you're correct? IDK and couldn't find a clear answer with my google-fu. I would have guessed that physical activities guided by vision would be the most demanding and engaging the most areas of the brain. But again, I have not found anything to confirm or reject that guess.