He was sent on a quest for the College of Winterhold. It is a Radiant Quest because the dungeon for the quest is selected at random. He arrived at the dungeon but could not enter at all beyond the first chamber. All entrances to the rest of the dungeon's interior are locked.
Why? Because to access that dungeon, you have to complete a Companion's quest (not a Radiant Companion's quest, but one of the main Companion ones). An item is required to enter the dungeon and it is only available during that Companion quest.
To me, it's an example of Radiant Story doing TOO much. Now he has to advance in the Companion's Guild, although he is playing a pure Mage and wanted to avoid the Companions until another playthrough. It throws a small wrench in the "do what you want, when you want" aspect of the game.
I apologize if this is old. It's the first example of something like this happening that I've heard of, though.

