We could perhaps say that the interactor is the author of a particular performancewithin an electronic story system, or the architect of a particular part of the virtual world, but we must distinguish this derivative authorship from the originating authorship of the system itself.
It's interesting to me the different definitions of authorship within games, as in many interactive storylines, the player is creating the path that the character follows, yet isn't creating the roads they use to get there. While the creator of the game sets the limits, the player is the one who truly creates the enjoyment of going through the game.