This is a good example of Dui-chagi. I
can tell you several points of this kick.
First: The kicking foot moves straight way.
Focus on the left foot of exampler, and you can see it moving
straightly like a thrusting a sword. It is most important of
feature of Dui-chagi. Compare this movie with this bad examples.
(3) . The (3) is quite
corrected one, but still you can see his knee of the kicking
Second: His turning and kicking is not divided.
I mean, kicking is a simple movement. Usually, many practitioners
kicks in two steps. (1) turn back, and (2) kick. In training,
this kind of step-by-step trainig is important and necessary
for exact pose and movement. But when the technique is achieved
it should be one movement.