I cant figure out why they want baking powder in that recipe. Baking powder being an acid based leavening agent that releases co2 into batter or dough without fermentation; it makes no sense to me that it would be in that recipe. Unless the recipe designer is after the corn starch.
Baking powder is a mixture of corn starch and baking soda. We usually only buy baking soda, if a recipe calls for baking powder I mix it myself by adding cornstarch.
If you dredge lightly the wings or duck, or fried chicken in corn starch, rice starch, potato starch you get a crispy, resilient finished product.
Do you think that is why they call for baking powder?