The Adamantine colonists must have found the Pre-CR system down here, and maybe repaired it, as a backup to their own systems. Then one day something had happened in the shaft they were using for storage and a piece of heavy equipment had hit the seal in the bottom hard enough to break it. A human had gone down there to check it out, and been contaminated by the alien remnant. The human had come up here, or been driven up here by the kind of compulsion Thiago had talked about, and had brought the contamination into this room where it had taken control of the Pre-CR central system.