You seem to be stuck in the (IMHO weird) idea of a user story being always something which is created by a business analyst making an interview with a user.

Sorry, but this is just a simplifying thought model, a simplistic example of how a user story might be created, but definitely not the only or the only correct possibility.

As I already wrote in a comment, a user story is just a sentence or phrase which describes a requirement from the perspective of an end user. 

- Who writes this sentence down is completely irrelevant. It could be an analyst, users by themselves, a developer, or any other kind of stakeholder. The person just has to "wear a user's hat" (but don't take that literally neither).

- If the requirement is found by an interview, if it is extracted from some existing documents, by analysing some UI of a competing product or completely invented by some ingenious person does not matter.

- This applies also for the different parts of the sentence.

So do yourself a favor and don't overthink this.