Ro's first appearance comes well before the Federation knew the Prophets, let alone the Pah Wraiths, to be literally real.

Riker calling out Ro for her earring isn't great, when compared against his acceptance of Worf's baldric. If I were trying to find a defensible reason, I might go with the idea that Bajor used to have a rigidly enforced caste system, and the earrings indicated one's caste, so it is possible that Riker assumed that Ro was trying to adhere to the old system which would fly in the face of Federation egalitarianism, and that he was less familiar with how Bajor's treatment of the caste system had changed during the occupation.