I've done it a few times, and the last time I tried it was on a beach in Australia. I have the scars to prove it.
You're attached to the kite through 4 lines, but there's a safety attachment that if pulled, disconnects three of them which lets the wind out of the kite. My guess is the guy got lifted, tried to pull his kite into "neutral" (putting it into a position where the least amount of wind can catch it) and allow him to slowly drop. It looks like he got hit with a gust and went face first into the sand, probably knocking him out. If he pulled his safety when he was 20 feet up he's going to free fall into the sand and probably break his legs, which although is preferable to smashing into a building it's not what is initially recommended if you get caught in an updraft.
Check out this youtube video where some guy gets pulled waaaaay up into the air, and floats back down because he knows what he's doing.
http://www.youtube.com/watch?v=6RuE5t1-H9k