I don't see anything wrong with his stride direction. But I would move him further to the glove side of the rubber to help avoid a late posture shift to the glove side.
Also, as the video progressed, the starting position of his feet got wider resulting in a bigger total body weight shift back towardds 2B. Keep the feet closer together to help minimize the weight shift.
Someone in the video keeps commenting about the front hip. Nothing wrong with the cue to drive the front hip to the target but I'd also want to see him lead with the front hip more - keep his head and shoulders slightly behind the front hip. (Hershiser drill)
Would also like to see him hold the front arm in an equal and opposite position just a bt longer. Or, get into foot plant quicker.
I agree with the instructor's comment about moving forward as soon as the front leg comes up. But I disagree with the instructor's comment about lifting the front knee straight up (assuming I heard that correctly). That isn't going to take away velocity. In fact, it might improve velocity if it improves his hip and shoulder separation. Future HOF pitcher Randy Johnson lifted his front knee towards his back shoulder and I don't think it hurt his velocity.