@sbrodhagen It's condensing a couple of different conclusions for a Youtube audience. The facts are: optimal growth occurs with 10-20 direct sets per muscle group per week, and the number of times you train a week doesn't matter
so long as you equate volume. So (on average) it is equally optimal to train 3 sessions per week and hit each muscle group twice (or really even just once) so long as you trained for like 2+ hours and got the same amount of volume as if you trained 6/week.
His ranges (4-10 sets per session, 2-4 sessions per muscle group per week) add up to around 16-20 sets of direct work per muscle group per week. He's not suggesting you do 10 sets of bicep curls 4 times a week, but that you do
either 10 sets twice a week, or 4-5 sets 4 times a week, because
volume equated it should give the same result.
Also its worth noting all the studies which show 10-20 sets is optimal were not on advanced lifters with dialed in technique working at 0-3 RIR, so likely those studies are not concluding 10-20
hard sets a week is optimal. It's much more likely an upper bound, and many advanced lifters on here will attest that they cannot recover from 20 hard sets per muscle group per week.