This is Cinavia audio watermarking. It's designed to survive lossy compression by staying within the human audible range.
> If a "theatrical release" watermark is detected in a consumer Blu-ray Disc audio track, the accompanying video is deemed to have been sourced from a "cam" recording. If the "AACS watermark" is present in the audio tracks, but no accompanying and matching AACS key is found on the disc, then it is deemed to have been a "rip" made by copying to a second blank Blu-ray Disc.
https://en.m.wikipedia.org/wiki/Cinavia
Edit: that same page says its now a requirement for all consumer bluray players to use this tech. But I don't remember seeing those messages for years. The pirates must be winning with their methods of changing the signatures.