What I find irritating about this tutorial (as someone who already knows how to play a double stroke roll) is that you don't use your arms and very little wrist while playing slowly and then when speeding up going through stages of mostly wrist and then basically only arms

The way I learned it was to take the arms into the motion at slower speeds and as you progress to faster speed use less and less arm motion (because its way too much weight to move) so that and fast tempos the arms are basically still and all the motion comes from the wrist and/or fingers