I'm not sure which part of the video the OP is referring to, but here are some things I saw:
In wrath's video, the rider is consistently using an extension movement at the edge change to unweight the board. You can see the legs extending just before the edge change, then flexing again to increase the pressure through the turn. This is sometimes called a cross-over turn, as the body moves over the board from one edge to the other.
Alternatively, one could unweight the board at edge change by rapidly flexing the the legs, then adding pressure through the turn by progressively extending the legs. The rider in blue can be seen doing this in the OP's video, though it's more subtle than the extension move mentioned above. Watch carefully around the 2:45-2:50 mark and you'll see it. I think this technique is especially useful in bumps. As wrath said, there is a slight upper body twist in the direction of the new turn in both examples.
2:38-2:42 is a good example/exaggerated demo of upper/lower body separation. The upper body is eerily quiet and static, while the lower body and board move around underneath. This is an effective technique for very short radius turns. It can be combined with the flexion/extension movements above, but is performed in isolation in this example.