There’s something important missing from this article:

Eventually, that same USB drive is inserted into an air-gapped computer, allowing GoldenDealer to install GoldenHowl (a backdoor) and GoldenRobo (a file stealer) onto these isolated systems.

Why is an airgapped machine running executable code from a USB drive? Is there some OS-level vulnerability being exploited?

The original writeup says the following:

It is probable that this unknown component finds the last modified directory on the USB drive, hides it, and renames itself with the name of this directory, which is done by JackalWorm. We also believe that the component uses a folder icon, to entice the user to run it when the USB drive is inserted in an air-gapped system

So we have airgapped machines that rely on users to click icons in a graphical file manager to move data from USB drives. This is a complete failure of security procedure. If you have systems that need to be airgapped then you also need the corresponding procedures for use of those systems to prevent this kind of compromise.

So they broke the air-gap bubble… do stupid things, win stupid prizes.