Yeah there's a "now playing" feature that will recognize music being played nearby, which I have found useful many times.
An AI note taker could actually be useful for some applications, like a meeting summary or play-by-play for a d&d session. It's just all the other stuff about AI that makes it shitty.
You can have it off and just use the "song search" on the top menu, but yeah. I assume it just keeps itself activated even if you disable it, they just try to be less blatant about catering to you.
Anecdotally, I've only had lime 2 instances of "google was definitely listening to show me this ad" in the 6 years I've had pixels, and I've seen just as many instances with other phone types. You truly have to go out of your way to avoid the surveillance.