@zawisza Rather than going down a rabbit hole of everything that is "scientifically wrong" with religious 'narratives', Christian or otherwise, I'd like to propose a thought experiment.
Suppose the 'Greys', because they're intelligent, also have religion on their world. Suppose they worship in buildings that have a cross on the front and tell stories remarkably similar to Christianity, even down to linguistic similarity of the syllables (keeping in mind difference of tongue). Or suppose they even know about Jesus and worship him. This would seem a remarkable proof of Christianity, right?
Or some theologians would say this proves Christianity is alien-derived and false. Or some would make innumerable other arguments from all sides.
Or perhaps the Greys even have historical proof to offer us from surveillance footage they took of our planet thousands of years ago. Then theologians can debate these new facts.
But equally the Greys could have a religion corresponding to Hinduism or Islam. Again, the same questions.
Next consider that the Greys may be the Christian Aliens but suppose we find later there are also Hindu Aliens. Or suppose they don't have religion yet we need to further study their notions of worship, their philosophy and their civilization in more detail to be absolutely sure.
Just that Aliens have a civilization somewhere is no more relevant to metaphysics than discovering the historical location of Atlantis is. Historians will accomodate themselves to it; likewise theologians will accomodate to the idea of an alien civilization, whether by calling them man or demon, etc.
There are an indefinitely large number of phenomenal observations for science to discover without ever coming to the end. Religion, insofar as its strictly adherent to metaphysical principles, concerns that which is absolutely true and unchanging. By definition, religion qua metaphysics is that which concerns the immutable. That does not mean that what religion says is absolutely true but rather that the domain of the absolutely true is the inquiry of religion (at least religion qua metaphysics and not religion as secondarily concerned with social questions).