I have a 3 year old who has all kinds of plans for Christmas. I seriously doubt a Raven is capable of that.
That being said, most atheists come from religious regions or families. They consider those holidays their heritage and celebrate them. Christmas is seen equally to, let's say, Halloween. Nobody cares about Samhain but they care about candies. Nobody cares about the birthday of Jesus but they care about receiving their family and giving them gifts.