Oh my god dude this article is so terrible.
Here's the thing about FM: John Chowning didn't invent it.
Any modular synth can do FM. ANY. Buchla was selling FM modules ten years before John Chowning stumbled across FM synthesis. If you have two oscillators, and one of them has a modulator input, you can do FM. But it generally sounds a lot like what you hear above - without some form of phase lock you get these gloriously atonal beats. Know why people went batshit for the DX7? Listen for the bong:
That is the clarion sound of a DX7 (more likely a TX816, 8 DX7s in a rack - I used to own one) doing what it does best- deep, round, lovely clangy synthesis. Problem is, it isn't frequency modulation (FM) it's phase modulation. That didn't stop Yamaha from selling it as FM - after all, as catalogued by the article, they'd been trying to come out with "FM" for ten years. All those notes between John Chowning and Yamaha? they're basically "Yeah, we did what you said in the patent and it sounds like shit. Any tips?" Chowning had none because, as noted in the article, he didn't know what the fuck he was doing.
Meanwhile, the rest of the world discovered chips, too. As mentioned in the article, NED put FM on the Synclavier (along with a dozen other kinds of synthesis, because Synclaviers are incredible, beautiful, agile machines). You'll note Yamaha didn't sue NED... Stanford did because Yamaha's technology at that point wasn't FM.
So the synth industry collectively rolled their eyes and called "FM" anything else. Casio called theirs "Interactive Phase Distortion Synthesis" and put it on the CZ1, CZ101, CZ1000 and VZ1 (I owned two of those). Kurzweil hemmed and hawed and said "technically, this is similar to FM synthesis, a process patented and vigorously defended by Stanford's CCRMA." I can't remember what Chroma called their version.
Realistically speaking, this is an article about a patent troll. It's been suggested that Stanford let John Chowning go because Yamaha was getting angry about their worthless patent license right about the time Stanford watched every other synth company on the panet successfully implement FM and then brought him back once the DX7 started taking off because it gave the DX7 the allure of "science."
Chowning discovered FM by accident ten years after Don Buchla and others had started marketing it in shipping products. Get a bunch of modules together and you'll stumble across it, too. His reputation among musicians and designers because he literally prevented experimentation with FM for eighteen years right in the sweet spot of digital synthesis.