In my University of Applied Science we got taught that user stories are a part of Scrum, and when reading things on the internet it seems that everyone indeed uses User Stories when using Scrum. The accepted answer at this question for even speaks of "Scrum User Stories", and the accepted answer of this question also mentions user stories are part of Scrum. Also, everyone I speak to at my internship company thinks User Stories are part of Scrum.
However, I can't find any mention of User Stories in the Scrum Guide. Only of "backlog items" which could be anything. Even "Design a logo" could be a backlog item, if I understand the Guide correctly, but that's absolutely not a User Story.
To what framework do User Stories belong, if they don't belong to Scrum? And what caused them to be regarded as a core part of Scrum?