> That...doesn't seem plausible.

In what way? Dramatically lower processing and signature complexity. Audio signature matching is trivial and extremely well known. I see absolutely nothing implausible about this, and it seems a robust, viable solution.

> This paper from 2024 investigated both Samsung and LG and found that they both capture screen images for ACR, and send the resulting hash (not the raw content) back to the manufacturer for identification.

That paper found no such thing. That paper actually demonstrated that they have no clue how the ACR happened, they just demonstrated that playing content yielded content IDs. It is more likely they were witnessing audio ACR happening, exactly as LG described.