Hmm. I don't really doubt that there's something more in this universe than us, or the multiverse for that matter. Truly, it'd be arrogant to think that only one planet out of the very, very, very many planets out there has managed to gain lifeforms.
There might be some alien race that has stumbled upon us at some point. We can't truly know, neither can we disprove it.
There's an interesting passage in the Bible that speaks of a special village in the mountains. IIRC, it's during the time Moses et al. walks from Egypt to what is now Israel. Two runners are sent out ahead of the group, to scout the area. When they return they speak of giant humans, I can't recall how tall they were supposed to be, but they'd still be considered very tall. (Think it was seven feet/above two meters or so.) The gene that causes people, both male and female, to grow to that height has been identified, and it's very uncommon. Some consider that gene to originate from the mentioned village. But they also say that it was unnatural for humans to be that tall back then, it has to be due to outside influences.
Whether any of that is true or not I can't say, but I remember seeing a documentary about it on Discovery.
It's also interesting to note that humans have started to come up with viable options for how to build flying saucers, options that would explain why they are always round in all stories. All we need to manage now is a propulsion system that works both in atmosphere and in space.
Humans need to wake up and smell the roses imnsho.