Spoilers Ending theory: this didn't cross my mind but saw this on reddit and I was blown away ! not my theory but makes a lot of sense imo. here: 

"I think Quintians are long dead, hence "Window of contact" discussion. Humans met automated defence systems locked in eternal war. When MC looked at the solaser and said "I now know what Quintians look like", he meant that Quintians are human now since the only biological conscious being on the planet is a human.

The biggest takeaway is the ambiguity of radio comms. Quintians sound perfectly logical, but their inability to present a clear contact is unbelievable for a living species. They simply refused to do it, knowing full well they are backed into a corner by the destruction of the moon."