Everything Adam knew about the Forgotten Mills, Ureyn, and Nollura came from only one person—Gareyna.
Adam was not stupid and tried not to believe every word of people he barely knew, but he did not always have the opportunity to verify the truthfulness of those words. He was in a new and unfamiliar territory with a complex system of factions, and each powerful monster had its own mill.
At the same time, he needed to somehow obtain the Connected Heart in order to ultimately create the Second Grand Star.
Obviously, in this case, he needed help and information. Unfortunately, Silvana no longer had detailed data on each territory, even with increased access.
Thus, Adam believed Gareyna's words and set off on his journey.
It was hard to blame him for this, because Gareyna did not lie to him about most things. There were three factions at the Forgotten Mills, the Gray Needle members were difficult to reach, and the Black Cut were threatening persons.