The 20 rep squat is not old school, although the 20 rep breathing squat was popularised by Peary Rader.
Back in the day and around about 5 Years prior to that time Dr Ken Liestner made popular the 20 rep squat, this wasn't just something you did on a whim the aim was as Bazza states, pick a weight that you can do 10 and do 20, and to improve over a protracted time, as you become more conditioned the pause between reps become less "metcon" it was usually part of a full body workout.
But the point I'm trying to make is whether you use 5, 10 or twenty you work it hard and do it properly.
Jesse was a strongman /powerlifter he did these workouts to improve his condition and strength in an efficient manner.