The problem has been fixed, but Bethesda’s marketing VP Pete Hines said on Twitter that he has “no idea” how it happened. “[Xbox Live is] not my platform. Bug/hiccup. They’ll undo it.”
The main game and all the existing downloadable content – Automatron, Wasteland Workshop, and Far Harbor – were all included in the mistaken price drop, and likewise have been restored.
According to Neowin.net, Xbox Support has told inquiring users that licenses for the game obtained through this pricing error will be revoked, so it turns out the lucky few weren’t that lucky. They’ll have to buy their copies of Fallout 4 just like the rest of us.