Oh, it seem's im the one who 'hasn't heard' then, so radiant story is just the set side quest's that are more tailor made for your charter's style?
Radiant Story is just the name of the tool they use to control certain aspects of a given quest. Todd is trying not to really sell it like they tried on Radiant AI, because, as it already has, it'll create a lot of false expectations.
The vast majority of quests are run through Radiant Story. Some may have only one "Radiant" Variable dictated by the tool, some may have several, but each quest is still actually hand-written.
A Radiant Story Variable might be the location of the dungeon you're sent to, or the actual person you obtain the quest from, but the actual scenario, and it's objectives remain the same. How I understand it, is, a Quest Writer comes up with an idea for a quest, the popular example is, rescuing a child who's being held for ransom. The writer then decides what aspects will be set as "Radiant". The Person who gives the quest, the location, and the reward in this case.
Radiant Story is set to favor NPC's with high disposition towards the player who already have a child. So, the quest initiates from someone who holds you in high regard. Radiant Story is set to make this a Challenging quest, so it puts the objective in an unexplored higher-level dungeon(hopefully a dungeon in proper context, for example, if the kid is being held for ransom, it doesn't make sense to be occupied by daedra or wolves), and the reward is set to be something the player can use, which, say your highest skill is Archery, it might be a new bow, or perhaps a quiver of arrows.
But the Overall story remains the same, Kid is abducted, need to rescue. That's just a blatantly generalized example to clearly illistrate what's going on with Radiant story.