They used a concave disk-like speaker to produce sound. This solid shape makes the sound waves kind of spin around themselves like a tornado or one of those bubble rings you see people blow underwater [1] instead of a normal pressure wave that goes in all directions.

The tornado sound wave can only move forward and once it hits something is dissipated and doesn't reflect the sound.

1. https://youtu.be/t2kvEC852MI?si=QJjinL7AK6ZZS_SO

It is a hotel revolving door for sound waves.

But the door is also a sound wave.

I've only skimmed the article/paper and I also dont' understand, so I'm just as ignorant as you, but there is such a thing as a Tesla valve that is a static object that allows water to flow in one direction [0]. I would assume that maybe they can make little vortices of air/liquid (as the comment by kylebenzle suggests) that are dynamic and create a similar structure as it evolves.

[0] https://en.wikipedia.org/wiki/Tesla_valve

A shockwave does not travel linearly.

Classical music while you're outside

Have to wait for them to discover girls, or boys...