As an historical sidebar, it's actually through pondering this very question we get our modern day belief in Extraterrestrials. Before UFO's and Flying Saucers, back in the very early part of the 20th Century, a group originally within the Fortean Society took to this very notion with great enthusiasm - they actually became the worlds first genuine UFO nuts in point of fact.
Fired by such stories and descriptions as Jacobs Ladder, The Ark of The Covenant, Angels, Voices from the Heavens, Sodom and Gomorrah, The Pillar of Salt, etc they really were amongst the first to espouse such views that extraterrestrial life may be something more than just bugs living out there in the great beyond, but actually fantastically advanced civilisations, eons old, capable of visiting our world and having done so in ancient times - largely citing such biblical passages as suited their beliefs.
Subsequent sightings of aerial objects originally referred to as "Ghost Rockets" became inevitably seized upon as being evidence of, at the time, modern day sightings of these very things - and proof, beyond shadow of any doubt, that the concoctions they had made based on biblical sources were in practice all absolutely true.
It was exactly such pundits whose views were to come to the fore immediately after the Kenneth Arnold sightings back in '47 - and this remains largely where we get our stereotypical archetype of the modern day UFO nut - someone seemingly incapable of distinguishing between what happens in the real world and what transpires only in fiction.
Much has been written about the UFO/Bible connection over the years, it remains one of the longest running themes throughout - largely unresolvable due to the fact that it touches upon subject matter, i.e. biblical text, largely accepted, literally in this particular instance, as Gospel and therefore considered valid for speculation.
Whether it says anything at all about aliens themselves, we are likely to never know - but one thing this particular line of reasoning does shed light on explaining is why the subject of UFO's and Extraterrestrials lends itself so readily towards the origination of multifarious quasi-religious beliefs - mixing the two ostensibly separate parts into a fluid and accommodating whole amongst those to whom concepts of spirituality and enlightenment remain important.
It starts with belief already accepted as such and elaborates upon it to encompass additional additional elements, the notion that God may Himself have been an astronaut not least amongst them.