Ground nuts are a common substitute for flour on Pesach. Ground almonds are more ubiquitous, but it does not surprise me that some recipes would call for ground hazelnuts instead.
Incidentally, ground almonds or hazelnuts mixed with melted butter or margarine makes an excellent Pesahdik alternative to a graham cracker crust, and is also useful year-round as a gluten-free crust. I like to use it for key lime pie, which is one of the few pie fillings out there that can be made Pesahdik without modifications to the standard recipe.