Apparently, this is due to Sidney being a "grandpa name" that is now common to give to girls. The Book cautions to not give these names to your boys, OH NO! Only girls get these gems:
Allen, Barry, Cyril, Gary, Howard, Ira, Jay, Lawrence, Maury, Norris, Perry, Roy, Sheldon, Theodore, Vaughn, Wallace, Wayne
Re: old man names to name your daughter
My husband wants the name "Charlie" if it's a girl! UGH!