Based on my kicking experience I actually think he intended to keep his leg bent due to the shorter distance. I was never taught to, but instinctively did the same. Once you throw a few hundred of a kick you really learn how to judge it's effective distance and how to tweak it.

>I'm amazed Uriah was able to pull that off
>since the leg than landed the kick wasn't fully extended. I'm
>sure the people that trained Uriah Hall in Tiger Schullman are
>very proud.