The Starworm seen ingame isn't the same one that visited earth before.
- If the Starworm is just what amounts to an alien space truck, it's entirely possible there's more than one, and the one we see is a wholly different one from whichever one visited us before. After all, it IS implied the One Concern existed for several centuries.
The Starworm isn't the only one of its kind
- At the end of the game, we learn that the Starworm is actually a giant mech piloted by a birdman. With that in mind, it's very possible that these birdman have been invading other planets in order to fuel their Starworms with ivory.
The One Concern was borne from the Starworm's mind cannon.
- The final stage of the game gives off the indication that it's meant to be a fueling station for the Starworm. There's also evidence it has been mined through to some degree. So, it's possible what kicked off the whole Concern was something like this: A miner, probably an early colonist, descends upon the fueling station after the (or even a) Starworm decides to make a visit. The miner pokes and prods at the "creature," until the bird pilot, annoyed, fires a shot from the "mind cannon." If you're familiar with any form of organized religion that isn't polytheistic, much of its development and origin tends to center on an individual attaining some form of revelation. Example of this being Moses on Mt. Sinai, Muhammad in Hira, Gautama at the Bodhi Tree, Zoroaster at the river bank, and more. Such abilities of revelation can also occur when under the influence of hallucinogens, particularly psilocybin. Inversely, such hallucinogens can also cause "bad trips," which may trigger a psychotic break. So while Royal, the Pupil who was attacked by Elro and exposed to the real world, and (to a lesser extent) Robin experienced "bad trips" under the influence of the mind cannon, this miner, who we can assume is The Father instead had a revelatory experience. Mixed with the advanced tech in the fueling station, he began organizing a religion around Ivory, which would become the One Concern.
Assuming konjak is up to it, there'll be a sequel that delves into a larger-scale first contact situation with the Birdmen.
- Considering that the final fight of the game is against one such Birdman, which was only barely hinted at before said fight, it would only make sense that fans would be left wondering just what exactly its deal was. As such, a potential sequel might begin with the Birdman's child, a full-fledged trucker-mechanic in their own right, sent to Fuel Depot 177 (i.e. the first game's planet) to find out what happened to all its "whitefuel" and why it's suddenly covered in absurd amounts of plant life. When a maddened Royal finds their truck, mistakes it for Him, and attacks it in a fit of rage, they end up falling to the planet's surface trying to fend off the intruder. From there, things escalate as our protagonist and their fellow avian kind realize that this seemingly ruined depot—and the "scavenging vermin" infesting it—are both far more complex than they thought.