[Djehngo]

I think the point is that USB vectors allow the malware to jump the airgap but not reliably, maybe it puts some data on a USB stick and jumps it back but for the most part once it is behind the airgap it will only do what it's programmed to do.

Being able to communicate via ultrasound means that if you have an infection on two computers either side of an airgap in close proximity the theoretically isolated computer can be sent instructions from a C&C server and can send data back at-will.

I'm not commenting on the legitimacy of the story, but either technique in isolation is of limited use, combined however they can be a lot more effective.