The hold he used was taught to him in his training.
I don't know about what police training involves so I can't comment on the actual hold that Chauvin was doing. The faulty training was the overall situation. I'm sure those officers have to take classes on how to deal with different situations, and I believe they even have to take some psychology classes as well. They need to be able to read the situation, and respond appropriately.
Floyd said many times that he had anxiety and claustrophobia, and the lady at the start of the video told one of the officers that floyd "had something going on up there". Sure, thats a bit vague, but, again, it all has to be considered.
Now, I know its going to be hard to keep everything straight, especially when so much is going on, and all happening so fast, but, when they heard "clausterphobia", "anxiety", and "i can't breathe", that should have sparked something in someone that "hey, maybe we should just let this guy stand up, as long as he's still"