I don't know all the details of this, but:
(1) The drone operators probably were breaking some laws when they commanded their drone to fly over somebody else's property, especially if the drone was not in sight of the operators at the time; but
(2) Discharging a firearm to disable the drone would seem to be an act that has ample potential to be dangerous. The flight path of the drone after being shot could not possibly be controlled and it could easily cause damage to property and/or injury.
Also, it would seem that the gun owner threatened the operators with shooting them. In Britain, that would rightly get you locked up. I don't understand why or how that's acceptable in America.
Both parties were in the wrong IMO.