Wars and Corruption!
They perhaps have observed us over a time period and seen that we do not seem to learn from our past mistakes of both corruption and having wars? Humanity cannot learn to end Genocide, as much as a fight between drunks outside a pub or at a match?
If they are out their, they will be aware that we have a mechanism within us that cannot be cured by our own trying to do good and perhaps they too are aware of sin? Since the Holy Bible tells us that when Adam and Eve sinned, so did all of creation fall!
They too would have a similar religious theology and would to be aware of this heavenly collapse, because what ever they call their god they would know that he created everything!
Genesis 4:7, Exodus 9:34, Deuteronomy 9:18, Matthew 19:28, Mark 13:9, Romans 1:20, 1 Peter 1:20.
Ask me and I will tell you! 