I'm no expert, so take this with a grain. I don't think what he does is unique, but how he puts it together is. Dragging the puck to the change the angle is pretty a standard MO for NHL players, especially when combined with a snapshot, but others tend to do it with their off foot like Phil Kessel to generate that quickness in their release.
But Matthews, he transfers his weight like a wristshot onto his orthodox foot, but instead takes a snapshot. This allows him to drop more of his weight onto the stick to flex it and generate power. Again, other player do this, too, but I don't think it's that common. I think its more common to snap it like Kessel does, and that helps with the deceptiveness of the shot. And when it's all combined, the quickness, accuracy, and velocity generated, it's crazy good.
I think it helps that he uses, I believe, an 80flex which is pretty whippy for his size, which helps him in getting that shot off quick.
The NHL has a video of him demonstrating his shot and talking about it. It's pretty interesting, especially if you're like me, and are constantly working on your game.