That's just what the Teishu thinks. If they're on bad terms, it's not like the Sage would necessarily give a shit about explaining himself anyways.

[Basically only the Sage would really know what the Sage wants.]

I don't know enough about magic to say for sure, but if this challenge thing was designed just for this, you'd think they worked it out so that it'd be guaranteed to turn him into some kinda purification powers. Besides, you said yourself he answers to some bosses of his own; I wouldn't think they'd waste their resources to let the Sage become a god just for kicks.