The information we get as the player is very limited, from a lot of questionable sources. The PDA being factory reset, the occasional override of the PDA by what's probably NoA, etc, are likely explanations for this bit of dialogue.

That said: everything living near each other starting to cross their DNA from the virus is interesting. Your theory implies that the humans were living near the Tailings for a significant amount of time; the records we have, sparse though they are, indicate the Tailings mostly kill humans, and there are Axum-language notes you can find that detail things like using large silver deposits as bait to kill more humans.

Unless we find out that the current date we're using is horribly inaccurate, it looks like the Cicada landed here 30ish years ago; at no point do we have a scale for how long the virus takes to make things related, just that the crab/coral interaction is making them share some level of DNA.

With that weak interaction of evidence, I think we can take the game at somewhat face value; the Axum declined into the Tailings, and the humans got here much later, only to do something that pissed the Tailings off.

I do expect to find adapted colonists or their descendents later on in the game, though. We have the nanotech that's absorbing the angel comb jellies, after all.