Not exactly. From my understanding, Bethesda is letting Obsidian make a Fallout game because they have people from Black Isle. I don't know who approached who about it though (whether Obsidian asked or Bethesda offered, I mean). Bethesda still owns the series though, and they are making a Fallout 4.
Well Pete Hines said in the OXM podcast earlier this month that them choosing Obsidian had absolutely nothing to do with them having Fallout creators there, though he could have been lying. But considering the guy didn't even finish asking the question before he started saying "No, no, nope," I wouldn't doubt he was telling the truth. :shrug:
I also recall, back when New Vegas was announced, Bethesda saying Obsidian approached them with the idea.
Well they're giving them the rights so they can make the game, a temporary license or something, but why wouldn't they simply make it themselves? Is their team..Busy?

They're busy twiddling their thumbs, slowly approaching bankruptcy, duh.