(Can someone post the link to the OP's video? It isn't showing on my iPad so I have no idea what it is.)
That looked more like control surface flutter than it did side-load-force. It can happen from excessive speed, a loose control servo mounting, or hinge failure. Either way it's the builders fault.
A few weeks ago someone posted this video. Eagle pointed out that the vertical stab or rudder failed first, causing the catastrophic series of events. Look up the thread if you can.
This is one of the most misunderstood crashes out there. Reader's Digest explanation...
The aircraft was built to certification standards. Pilots erroneously believe that when at or below Maneuvering Speed (Va) they are protected from structural failure when applying full flight control input. This is only PARTIALLY true.
If you apply full rudder in one direction then full rudder in the opposite direction you have no guarantee the airplane will stay in one piece as the certification rules do not require this.
The First Officer was the flying pilot and apparently got to dancing on the pedals in turbulence. The vertical stab failed as a result.
