I’m not a huge expert on the Alien universe, but I think the idea is that in the original Alien movie the corporation that owned the ship did already know about the Xenomorphs somehow, the distress signal was a ruse or an excuse to send them to the colony with the eggs, and the secret synth Ash had been tasked with bringing a Xenomorph back at all costs, over and above the safety of the crew. So, in light of that, it’s not a stretch to think they already knew about the Xenomorphs in ‘Alien: Earth’, which takes place, I believe, 2 years before the events of the original movie.
Plus, some Noah Hawley retconning may be involved. If you haven’t seen it already, there’s a long Alien: Earth thread where some posters get pretty in-depth with Alien lore and canon.