Some might conclude (as we did) that we simply didn't have enough information to reach an explanation. But others may conclude they were extraterrestrials, or interdimensional, craft. Others might immediately conclude they were secret government aircraft, or some that they were simply hallucinations. But code can only conclude they were simply unidentified, without eliciting the least curiosity afterwards.
You completely described a coded thought process that could easily be implemented into AI. You have information inputs in your brain of aircraft, secret government projects, and aliens. When you saw what was flying over the skies, your brain accessed all information it knew about flying machines. It pulled out airplanes, government projects, or aliens. Then using that information, based on all life experiences and other factors and beliefs, it came to it's conclusion.
Were you a robot with AI intelligence, the input would be the UFO's you saw, UFO simply unidentified flying object. Having taken in information as an AI life, you would have known about airplanes, secret government projects, and people's beliefs in aliens. Your code would have analyzed what you saw and the only 100% probability would be as you said, simply unidentified, but to give a more specific answer it would use all available information to create it's most likely conclusion or 'belief'.