It is when, where and in what spirit, I believe Darrin was making a point about. If there is an evergreen tree in the room; if there are lights on it. If the paper is, predominantly, green and red; if there are certain seasonal songs playing in the background, then, yes, those atheists are, in fact, not just exchanging gifts, but are taking part in the celebration of the birth of Emmanuel, the Messiah, the Prince of Peace, King of Kings, Lord of Lords, Redeemer and Savior, Jesus Christ.
If you, Chumpdumper, just happen to walk over to your parents house sometime in the next month and hand them a present, saying, "I thought you'd like this". Then you get a pass.