This is an example of losing his control of turning back.
It is very common problem of beginner when he tries Duichagi.
Duichagi actually uses the power from turning the kickers
body, but his intention should not be that.
The kicker should intend to turn back and kick back, in ther course of
fast kicking(turning his body).
Otherwise he will lose his control on his body and turning and will move
like this example.