Human brains are really poor at interpreting new brief visual stimulus "correctly". Furthermore, our first impression can affect the perception of the stimulus even if it lasts several seconds.
I'm 36, and visually quite acute. I've seen my visual system doing the craziest interpretations in various situation, and observed my interpretation of a visual field completely changed by a sudden re-interpretation of some small detail.
Given proper conditions I could have interpreted these as apparitions, ghosts, materializations or whatnot. The difference is, all of these situations happened in calm mundane situations where I had the luxury to pause and look at the thing for a long while and figure it out.
The craziest was a low-lit room where I saw the patterns of a carpet as my son, walking. I had woken at night and presumed it was because my kid was awake. When I came closer I realized it was the carpet.
If I can mistake a rug for a human being I do not find it unlikely that a pilot trained to be aware of bogeys to interpret unexpected stimulus first as a vehicle (this interpretation is very hard to shake off).
In this Mercury 7 astronaut, former pilots, retired air force officers, Major Generals etc give account of UFO sightings.
Although produced by History Channel, it features only accounts of these distinguished people and recollect no spin (if my memory serves me right).
[0] https://www.youtube.com/watch?v=jTEZeY-fNCU [1] http://www.imdb.com/title/tt1579236/