Am not certain but Sweden may have a system like they do here in Norway. you are automatically a member of the state church unless you actively get yourself removed from the membership list. My wife and I have never belonged to the church here. she and her father both opted out (so she wasn't a first generation non-believer) Nevertheless during a routine check through some papers we discovered that someone had taken the liberty of having my youngest listed as a member of the church
It's the same system in Finland. Naturally that made me curious. Are all these people atheists who are too lazy to unregister? So I have been asking around. Most are believers just on a very low level: 'there has to be something'. Some are atheists.