So remember he talks about the type of training that lead him to his size, not the type he did after he got it, that is what I used. That usually involved 2 sets to failure, not just one. A second set was done with a short rest period that is about 10% lighter. It was VERY effective for me and still is. As I got stronger and bigger, I went down to a single set. Every time I applied more strict HIT principles, I got results from it. That being said, I don't necessarily apply strict HIT principles to everything. I still do 1-5 "warmup" sets too...
Don't forget this: Dorian didn't do a single set because he was worried about overtraining, it was done in order to increase the intensity, there is nothing more intense than knowing you only have one set and you have to put absolutely everything into it, THAT leads to muscle growth.