The Agharinists worshipped Sartan as one of their gods. They called him a different name, but they recognised him as the same god the Sartanians worshipped. I'm surprised you didn't know that.
Nah, that was a recent development. I remember during the fall of Niel that their high priest did an RP which made it clear that Adgharists considered Sartan to be dead and gone forever - they only decided to sort of recognise him as part of their pantheon after Sartania fell. Before that they insisted that he wasn't a god at all.
So basically, Sartanians never believed Adghar existed and the Adgharists only considered Sartan to be part of their pantheon until recently.