Here's another brainstorming post.
Unlike humanity, the yinrih don't have a concept of native or indigenous peoples. This is especially true on worlds other than Yih which were terraformed from lifeless rocks and populated by yinrih from scratch. There are a lot of groups that appear to be uncontacted tribes, especially on Sweetwater's many islands and floating vegetation rafts, but they all started out as bands of Atavists, Primitive Wayfarers, Neoshamanists, or other miscellaneous groups who chose to isolate themselves from wider yinrih society.
If you've ever seen the movie The Village, that's how these groups start out. A group of people claims, buys, squats on, or takes over a difficult-to-access bit of land, then forms a group of childermoots, becoming a little insulated shire. They tell their pups that there's nothing beyond the trees/waters/mountains/whatever, and over time history becomes legend becomes myth.
Some residents of the Spacer Confederacy or Outer Belt have the moxy to do this on an orbital colony, which results in a ctrl+C ctrl+V of every sci-fi story about generation ships ever. i.e. the residents believe the colony is the entire universe, with upkeep of the ships systems handled by “machine spirits” (leaseminds and drones) or by a cargo cult.
Before First Contact a subculture of regular yinrih existed that was interested in these self-isolated cultures. The first Terraboos emerged from this subculture after First Contact.
Given what Neoshamanists believe about the noosphere and consciousness, they'd be the ones of all yinrih groups to try for strong AI. They don't get there, but perhaps they pioneer things like machine learning algorithms and leaseminds.
Yet another theory about Yinrihcron™ is that it was built by a group of neoshamanists trying to make an AI god.