i think it's pretty obvious that this was a bear raid to trigger stops in a thin market. Someone smashed it down, triggering stop-losses and picked up a bunch of cheap coins. Yes, some standing buy orders will have been filled, and a few lucky people got some cheap coins too, but overall mostly people got raped and one entity made a huge profit.
All happened too quickly for any new orders to be placed.

Was it done with inside knowledge of the order book? Quite possiblly, but we will never know. Could easily have been the exchange itself.

I don't buy any 'fat-finger' theories. Rape and pillage much more likely IMO - this is Bitcoin ...

Just my 2c