That's an entirely different kind of attack. If your server is being flooded with 20TB/s of traffic, there's nothing you can do on the box itself to fix things. Whatever you do, the legitimate requests won't be able to get through.
If however your DOS attack is an attacker making lower-volume CPU-expensive requests on your site, there's plenty of things to help mitigate the assault.
That's the key difference between a DOS and a DDOS, yes. Since I can't load the OP article on this machine for some reason, I can't review the symptoms described. The title of the article does say DDOS, however, which is focused more on saturating bandwidth, not CPU.
The headline and article itself do indeed (incorrectly) call it a DDOS attack. The attack itself was very much non-distributed, and involved a single malicious actor `curl`ing an expensive API endpoint in a loop.
If however your DOS attack is an attacker making lower-volume CPU-expensive requests on your site, there's plenty of things to help mitigate the assault.