I think the GP meant that in theory someone could break into a Bluetooth connection and snoop on your phone calls. But with a wired headset, there's nothing to break into. "Unbreakable encryption" is a bit tongue-in-cheek, there.

> there's nothing to break into

Wired headphones are giving off EMI of the signal they're playing, one could sense that signal with the right equipment and know what you're listening to remotely.

The advantage here is that you need a physical connection to decrypt the content.

Eh... If your adversary can break modern bluetooth encryption, I probably... would not bet on this? I would think that with appropriate radio equipment you can probably pick up audio from many wired headphones.

bluetooth encryption has been broken before. "KNOB" (https://www.usenix.org/system/files/sec19-antonioli.pdf) was less than 5 years ago. The kind of equipment that could pick up the audio over a wired headset from across the room could probably pick up something from the speakers of wireless earbuds too.

I wonder if there are attacks based on RF emissions along a cable to get the sound

Yes, there are. You can even get video signals from a video cable.

Not if you have a good microphone and the sound is loud

That's not a failure of the protocol but of the user. It's like saying PGP for email can be broken if you have a telescope to look at the user's screen.