> In an agile game development user stories are used in the sprint backlog.
If you want to go by the definition, then user stories are one type of product backlog item used to populate the product backlog. A set of user stories (short descriptions of what a player will do in your game if the feature it describes is implemented) that are to be added to a game within a sprint is called the sprint goal. A sprint backlog is that goal plus the plan to achieve it within the sprint, usually in the form of tasks or however you plan your work.
This isn't how you *have* to work using agile, it's just the agreed upon definition.
Like the others, I haven't heard of user journeys, but in games there is often a need for larger constructs of user stories that bring together a narrative of features for the player. I'd encourage exploring user journeys.
Here are links to short articles about other narrative structures I've seen used: