That's an offensive drill where the defense is basically just dummied up. Purpose of the drill is to 1--Get the defender UNDER the level of the ball screen so the defender can't get between the screener and the handler. 2--Space and punish the switch. If the switch plays off (as in this video) the read is the step back 3 you saw. If the switch presses up on the handler, the read would be to isolate and drive past the bigger/slower defender. That's not at all a competitive drill, much more geared for teaching offense.