It makes a lot of sense to me in the realm of experimental and classified aircraft. Easier to leak junk designs and call sightings UFOs than keep things secret squirrel. According to the CIA half of the UFO sightings in the 50-60s were U-2s and SR-71s.[1] There's plenty more too, like the tacit Blue, RQ-3 Darkstar, FDL-5, and GD sneaky pete that sure look like "UFOs" to the untrained eye.

[1]https://www.popularmechanics.com/space/a3995/4304207/