I'll provide some links that mention it in a bit.
"5.1 A Potential Team-Up of the Big Three of Earth One" -
http://www.dccomics.com/blog/2013/05...n-to-earth-one
"5.2 The Earth One Line" -
http://www.dccomics.com/blog/2013/03...the-multiverse
"But these aren’t one-offs. We’re talking ongoing series of OGNs in a new continuity, on a new Earth." -
http://www.dccomics.com/blog/2009/12...e-to-earth-one
"We’re planning on doing two novels a year and set in this new universe, we’re getting unlimited creative freedom that we couldn’t have in current continuity." -
http://www.aintitcool.com/node/43302
without a doubt, the Earth One line was planned as a shared universe with no continuity. Teen Titans: Earth One just isn't linked with the events of any other books yet. What happens there doesn't affect any other book, but it 'is' in the same universe. If they do have a team-up or crossover, it'll be like how the JSA and JLA both first started - just took a bunch of characters who were being published at the time and threw them into a book together. the continuity comes later.
and it's where there aren't any adult superheroes "yet". thats pretty vague and telling at the same time. before superman? before batman? before they become well known public heroes?