- the drones were flying high. Show me any sharpshooter that can shot down a highly agile and impredictible target at 200m high. Clay pigeons are shot at 60m on a very predictable trajectory, and even that requires a lot of skill and training.
- drones flying on preprogrammed path are impossible to intercept electronically, with the exception of GPS spoofing. Even that is difficult, never mind deploying GPS spoofers around the airport
- it would make the airplane operations impossible, so can't fly while the GPS spoofers are running, and when they're not running, there is drone flying
- the complexity of keeping drones in the air for long times (replacing batteries, field repairs, having spare parts) is not to be underestimated. This suggests a planned operation