I refer you to a wikipedia article on "expectation of privacy" in which appears the following:
"In general, one cannot have a reasonable expectation of privacy in things held out to the public. A well-known example is... ...what is observed pursuant to aerial surveillance that is conducted in public navigable airspace not using equipment that unreasonably enhances the surveying government official's vision; anything in open fields..."
Note that the limitation on "unreasonably enhances the surveying" applies to government, not private, surveying. I think we can both agree that its a good idea to keep the government, with its vast resources, out of close surveillance of citizens without a warrant. The whole article is worth a read. It's worth knowing where you can expect privacy and where you can't. For instance, the article says you can expect privacy IN your home. There was no assertion by the shooter that the drone was hovering outside his window looking into his home, only that it was hovering over his yard. Another point of contention is how high the drone was. The shooter gives what may be a self-serving estimate of 20 feet, although he as no way of measuring accurately. The drone operator says it was much higher, and may actually have more objective info, either from GPS data or an analysis of any video he may have captured. I don't know, and neither do you. But the FAA has recently asserted control over all airspace from the ground up, so that would seem to make all the airspace at least controllable in a public way. One may not like it, but that's the law.