It is a random thing that happened with your llm, in my experience, it never mentioned anything religious.
Keep in mind that npcs after discussions that lasts more than a single exchange will absolutely tell other npcs something that depends on the contents of that discussion, if one npc speaks about religion to the others, I could see other npcs deciding to keep doing that.
Not really as I said npcs create prompt components for other npcs, ais knows that when there is religious context, more religious things appear, then it just increases in mass, it would happen even if you made a modern setting, it is related to npcs reasonings propagating from npc to npc, you can in fact also have them break and write only seemingly random glyphs for similar reasons and there was someone who reported their npcs all throwing random unreadable garbage.