Besides being really cool to watch, this scene is actually really important to the storyline of Scott becoming an alpha. He has so much more control here than in any of the previous seasons, and is clearly much more in control than Boyd and Isaac, who still “turn wolf” at random moments when they get emotional. You can see the exact moment that Scott decides to turn; it’s a very conscious decision on his part, and it comes in stages. First the face structure/facial hair bit, then the teeth, then the eyes. It doesn’t look the same as his other transformations, either - those were instantaneous and often instinctual. Here it’s like he’s pulling his wolfness out of himself, if that makes sense. The wolf is inside of him and a part of him all the time, but he decides when to use it and to what degree. Scott has an intense level of control over himself and the wolf, and that’s what allows him to have such control over the others.
Whenever he pulls the ‘alpha’ card on the others - with Isaac, mostly, but also Boyd - it’s always very deliberate, even in the heat of the moment like when he was trying to save Allison, and he uses the exact amount of force and heat needed to get the message across.
Scott knows exactly what he’s doing when it comes to being a werewolf, now. It’s not like in the first season, where he had to piece stuff together from Stiles’ internet research, his own instincts, and random bits of info Derek gave him sparingly. He still doesn’t have all the answers, but it seems like he’s just decided to come up with his own and just roll with what fits best for him - what seems right, and Scott is always trying to do the right thing. Scott McCall is going to be an amazing alpha, and we all get to watch it. I can’t wait.