There aren't nearly enough technical details provided in that article for my taste. Something seems a bit off.
they looked more like signal conditioning couplers, another common motherboard component, than microchips, and so they were unlikely to be detectable without specialized equipment.
"Signal conditioning couplers" aren't, to my knowledge, common motherboard components. I can't even think of why you would put one on a motherboard to begin with, let alone use it as a disguise. A passive component isn't a good choice if you're attempting subterfuge of this type, since it wouldn't generally be connected in a way such that it can both harvest the power it needs, and also alter signals on the board.
It would be much simpler to implement (and harder to detect) if they used an active component. For example, if they replaced the flash chip that contained the BIOS with another chip that appeared identical, but contained "special logic". No extra component on the board, and more die area (chip real estate) to work with. Or maybe they could just skip the fancy hardware altogether, and load the motherboard with an evil BIOS?
And you wouldn't need specialized equipment to detect this type of espionage; it whould be pretty obvious from the extra network traffic. They said in the article that the device didn't have much memory, so it needed to get further instructions from the network. That sort of traffic should set alarms off all over the place for any half-competent security admin.
The lack of corroboration is another red flag. Severe, widespread security problems, when they're disclosed, tend to be widely confirmed (see: Meltdown, Heartbleed). That does not appear to be happening here.
It's possible that the article author didn't understand the material he was reporting, or was intentionally dumbing it down for his audience, but something here does not add up. The described attack vector is simultaneously more difficult to implement than it needs to be, and too easy to detect.
The question of who would want to make up a story like this, and why, is
above my pay grade left as an exercise for the reader.
Disclaimer: I don't claim to be an expert on any of this stuff.
