I’d like to shove three oars in, please:
1.Any creature depicted as humanoid in that it has a trunk, two nether limbs and two upper, a neck, head, two eyes and ears and a nose is not an alien from another planet.
This should be obvious. The human form is the result of 3,500,000,000 years of countless random mutations, each one dying, surviving or flourishing according to the environment in which it was born (natural selection). It is quite out of the question that any similar path could have accidentally been followed elsewhere.
2.That aliens would be more advanced than us is a serious probability. If you depict the age of the universe as a line 2½ miles long, then each foot represents a million years. On Earth early man separated from the chimpanzee a mere six feet from the end of that 2½ miles and modern man appeared about 1 inch from the end. Technology started about 1/5000th of an inch from the end and we went into space about 1/20,000th of an inch ago. There is no reason why alien technology should have appeared so late in the day. Even a mere one foot ahead of us – a million years – would be mind-boggling.
3. A UFO is just that, an object that the observer cannot identify. If someone else comes along and recognises it as an aircraft, a weather balloon or the planet Venus, then it becomes what you might call an IFO. If there is no such second person, and the first person has no first-class photographs that can be analysed, then it remains a UFO.
How and why the leap is made from UFO to alien spaceship is beyond me.