Legally, I believe that this incident will come down to the matter of a lack of a NOTAM being filed by the organizers of this event.

NOTAMS are issued for any irregularity to the published conditions of an airport - even down to something as minor as an inoperative taxiway light.

Because there was no NOTAM in effect for this event, I believe that any rulings that may come down from the FAA or NTSB will find fault along the lines of an inappropriate use of a remotely piloted model aircraft at a active airport.

I'll revise my comment on what the lesson is here:
If you are going to operate an R/C aircraft, it is YOUR RESPONSIBILITY to KNOW and COMPLY with the requirements of the environment where you are flying.