This isn't revealing "Ethernet cable traffic contents". This is using crafted data over the wire to produce specific measurable (low bandwidth) RF emissions that can be picked up externally. It's obvious that this would work, and doing a proof of concept is a weekend project for anyone with an SDR.
Just like that "RAM as WiFi transmitter" (not really WiFi, just radio noise) and the previous one with GSM (same story) and all his other covert channel papers, this is completely boring stuff that requires malware on the sending side to leak data. His papers are superficial and he never attempts to measure maximum practical channel bandwidths, or do any other useful science. He's literally getting hundreds of times lower bandwidth than what would be theoretically possible with his approaches, because he doesn't actually know how to use proper encoding schemes or optimize his receiver/demodulator. It's all extremely low effort.
Every time he just comes up with a random idea of "something that can be measured externally from a computer", from spurious radio emissions to temperature to LEDs, then makes the minimum viable PoC to encode data over it and measure it externally, and cranks out a paper. Every single time. He's running a paper mill, nothing more. None of this is useful research, anyone can come up with his ideas and test them in a few hours. And he's really good at getting a news cycle out of it through misleading clickbait titles; he's really taken a liking to that recently.
All this air-gap jumping nonsense he describes only applies if you already have malware inside your air-gap. And if you do, well, the only way you're going to be able to stop leakage is to put the tainted computer in a concrete bunker surrounded by a Faraday cage and running off of isolated batteries. This isn't news.
FWIW, his clickbait theme was one of the things that inspired me to release https://M1RACLES.com the way I did. It's sad seeing real infosec issues getting mixed in with irrelevant clickbaited stuff that nobody cares about. And it works; a whole bunch of news sites didn't even bother to read past the first page of that site....