Thank you for putting more context into that! I was a bit confused at first.
Ah! That sounds a bit better. I could see children calling their grandfather or older family friend that.
Daddy/mummy/auntie/uncle/cousin/sister/brother pretty much indicate age/seniority/importance/familiarity in Nigeria without necessarily saying much about actual blood relation.
So the use of "daddy" in itself is just cultural and nothing specifically to do with the church.