I find it hard to credit the explanation of UFOs as all being ours. Granted, some are, but other aspects of the UFO phenomenon exceed that explanation. There are centuries of sightings before electricity was even in use, persistent reports of alien abductions, and UFO intrusions into military airspace and close surveillance of and interference with nuclear weapons.
Most of the pre-1947 UFO sightings are stuff like ball lightning, swamp gas, meteors. There are about 1/1000 of the quantity of reports as well [other than the ufo flap of 1890s which was obviously a privately built dirigible].