Could it have been a mass psychosis? First a real drone sighting and the closure of the airport; then when the news spread, tens of people reported more sightings. There are two densely populated towns on both sides of Gatwick airport, within a couple of kms from the runways. After the first sighting, any other within that range must have been considered a risk worth closing the airport for. A drone is just a black dot in the sky, I wouldn't be surprised by false reports.
