What is this effect causing a flash on video when a model aircraft collides with the ground?
Meet the power plant for the Nutball UAV. It contains, among other things, a servo, a killer brushless fan motor, and a 2.4 GHz spread spectrum receiver.

Without having the ability to perform a physical experiment, we have to perform a thought experiment. The battery recommended for the pod has no controls, save the speed controller for the prop, which is not particularly checking up on the battery pack. Similarly the IR receiver is not concerned with the battery, except to use it.

So, what exactly happened when the loaded brushless fan motor suddenly gets halted?

Well, the battery cannot instantaneously respond to the change - it's simply not possible. Not that there's a whole bunch of energy there, mind you, just a rapid transient in supply voltage. As the transient subsides, the chemistry in the battery hardly noticed.

So we have established the conditions, and we have to ask ourselves; is it more likely that a catastrophic voltage occurred during a disconnection that left the craft operational, or is there a more efficient pulse generator on board the aircraft?

It turns out there is. A radio receiver isn't physically all that different from a radio transmitter, and a spread spectrum system has more bandwidth than, say, an ordinary AM radio. What's more, the one on this device is already tuned for 2.4 GHz operation.

From the EMP wiki;


  An EMP arises where the source emits a short-duration pulse of energy. The energy is usually broadband by nature, although it often excites a relatively narrow-band damped sine wave response in the victim. Some types are generated as repetitive and regular pulse trains.


At the moment of the flash, you just happened to be incredibly close to a sharp change in voltage that was being passed to a broadband antenna, filming at a rate high enough to notice it, and pointing several megapixels worth of small antennas at it through the only part of your phone that would be able to notice that it happened. 

Now go buy a lottery ticket and share it with me.