Well, as I said above, the most obvious place you see this movement is in Biu Tze. For example, following the sideways upward whisking arms (sometimes called fak-sau, sometimes man-sau, etc.) you drop your elbow and forearm in this manner, and then proceed into the three turning kau-sau movements. It appears again in the next Biu Tze segment that begins with the three biu-tze-sau strikes, right after the fak-sau as you bring your arm back to center. It's not a "hidden technique" by any stretch. It's just uncommon to see it used in flurries the way KK applies them.
As far as Hunter's comment about power or the lack thereof, all I can say is that when I strike the wall bag with this, the whole wall shakes. And it's a brick wall. I swing my arm in a very relaxed way using elbow and body force, kind of like the turning fak-sau in Chum Kiu, except downward, sinking my weight. Of course my execution is influenced by the time I spent studying Escrima under Rene Latosa. At any rate, it seems to me that it is a very strong strike.