They didn't get hit. Not even once.
How is this possible?
Of course it's possible. We live on the internet now. People do insane things, particularly with Dark Souls.
But this is particularly insane, because The Happy Hob only recently beat the original Dark Souls without getting hit. I'm amazed that this guy has unearthed the secrets of Dark Souls 3 so quickly, to the point where he could pull this off. Pretty amazing.
You can watch the whole thing above. But I recommend jumping to roughly 9:08:00, towards the end. Just to see the reaction when it all goes down.
Or you can chill out for 10 hours. Your choice.