Yah, I don't understand that.
I've seasoned pans. You shmear oil all over, and then heat in oven until it's dry. How is that not chum d'tzli?
I'm not entirely sure, but this may help.
My understanding of the seasoning process is this: if the 3 parameters (thickness of the oil, temperature and time) are met, the oil will polymerize into a "plastic" that is nonstick and a rust barrier.
linkIn that case, it would be like using any dish made of plastic, where you do not need a hechsher on the
oil that is it made from.In essence, what you buy from the factory would be a plastic coated pan, and it shouldn't make a difference that the coating started out as edible oil.