It's also worth pointing out that simple application of logic could provide answers for this question. Firstly, by definition, a UFO is a flying object, and while mankind as an entity has learned how to fly, an individual man can do no such thing. So the first difference is that one can fly whilst the other cannot. Secondly, by definition, a UFO is unidentified. The question identifies the former subject as "an intelligent man". So the second difference is that one has been identified whilst the other has not. Thirdly, by definition, a UFO is an object, and how dare you objectify men! We're people, who deserve love and affection, and we should be treated right! ALL PRETTY BOYS DESERVE TO GO TO A BALL. To understand the differences between these things, one doesn't and indeed shouldn't rely solely on their powers of observation.
Seriousness aside, now that this is a Thunderdome, can I make another Paint monstrosity?