The interesting question, to me, is whether or not it was actually flying below the treeline. From TFA, the drone's owner presented flight data showing that the drone was not below the treeline, but the man who shot the drone down had two eyewitnesses saying it was lower. If we have altitude readings and video footage, it seems to me those should be able to trump eyewitnesses (assuming that data is complete and not suspect). That's why people are pushing to put bodycams on police, for example.
He shot it with birdshot from a shotgun. If it was above the treeline its doubtful he would have been able to bring it down with such a shot. Hit it? Maybe. But the further the range the less damage and more spread out the birdshot is.