For those interested in hearing some beats, the terminal demo starts at 4:34 https://youtu.be/vfgySTaM1TI?t=274

Those who recall cars with fm radios and gsm phones will have heard something similar if their car had a random compartment right below the stereo.

When a call came in, before the phone would ring, the radio would emit this very clear tri di di dit dah dah. But only when the phone was very near the radio.

Yes kinda, I would say network activity rather then traffic. Audio signal is going to be in scale of 48Khz while measuring ethernet signal at scale of 100Mhz. At that rate it wouldn't even get more then 1 sample from a full size packet. So really it's polling 48Khz whether or not there was activity during that period. The gimmick is that it uses some analog components. Fully digital you could craft a meaningful audio signal that represents traffic.

This is a fun demonstration of the principle.

"every website sounds different" - that's super cool.

The bitmap images sent at the end of the video also sound really cool.