User blog comment:Jimeee/PS3 release dates for Dragonborn, Hearthfire and Dawnguard - Euro Update/@comment-3428817-20130228200007/@comment-24.253.8.98-20130228200807

That's probably why Dragonborn was released before Dawnguard for PS3. Because the radient system doesn't care where you have or haven't explored yet. If you have the Dragonborn DLC then a radient location is possible in Solstheim.