Cellador is alongside Marsh and Yarwyck when they go to address concerns from Marsh and Co.
Septon Cellador cleared his throat. “Lord Slynt,” he said, “this boy refused to swear his vows properly in the sept, but went beyond the Wall to say his words before a heart tree. His father’s gods, he said, but they are wildling gods as well.“
Is Cellador’s opposition towards Jon based in part on being prejudiced towards those who follow the old gods or as he calls them "wildling gods”?
Absolutely.