The issue is more complicated, even if you're an atheist (I'm not but that's not relevant). Soul can mean more than something that lives on past death but a certain Greek "spark of life" which renders something a person.
You are correct that the Greek word for soul is actually better translated as "life-force".
Ancient Greeks believed in the afterlife, so they believed your essence survived death. They just weren't sure what that essence was.
I tend to agree with those that say we don't have souls. Therefore I don't believe Data has a "mystical" soul either.