Going with this route, I have a baseless theory:
“Bel’shir” is a microbial parasite with a very weak hive mind living in the terrazine under the planet itself. When you inhale the terrazine you become the host for your own little colony, but since that colony is no longer connected to the rest of the hive, it starts to diverge based on your own personality.
Stetmann kept inhaling more terrazine, adding more of the microbes to his personal colony. Since the new microbes would always correct his personal colony to bring them back inline with the main colony’s goals, he mistook that for revelation from Bel’shir.
The main Bel’shir colony wants to infect terrazine supplies on other worlds, which is why it sent Stettman and the ghost offworld. But since neither one is near Bel’shir to inhale more colonized terrazine, their personal colonies are going to diverge sooner or later