So, for my granny's recipe, no this isn't a mistake. Due to the fresh coconut coating the frosting, she didn't call for any in the cake itself. It isn't necessary for flavour. If you do want to add coconut in the cake, you can. I have added about half a cup straight to the recipe below without issue. If you are using a fresh coconut, you could use some of the coconut milk and coconut in place of some of the soured milk to carry through more of the coconut flavour. A touch of almond extract also pairs nicely with coconut.