I doubt that this is some awful conspiracy from Costco. I worked as a Pricing Team-leader for several years; and you would be amazed at the labels in a store’s computer system. That being said, I think this is a missed opportunity to consider the sensibilities of the very costumers who would be buying this product. You just might sell a few more Bibles by respecting, or at the very least tolerating, the beliefs of the customers that you are hoping will buy this product.
I had a pagan friend who was thrilled about the Bible being listed as Fiction. I had to point out that “sauce for the goose is sauce for the gander” — how would he feel about pagan books listed as Fiction? I suppose that the real question would be, if this was an error, would Costco have allowed this error to go this long uncorrected with the Koran?