Have you read the first book of "A Song of Ice And Fire", better known as "Game of Thrones"? Or the first book of "Wheel of Time"? The first one, two books of the "Foundation" series? Or the first few chapters of "Lord of the Rings" or "The Hobbit"? They're ok to fucking boring but very essential to set the world, to introduce characters, to help us imagine and understand the world the story is set in.
Sure, it's a bit unusual for an exposition chapter to happen in the middle of a story, but from what I know from the LN, this is sort of a moment where the story "gets broader" as Charlotte begins to learn more about Aoyagi and for that, an exposition is needed. Can it be done differently? Probably, but if you expect every chapter, every book of a story to be action and progress without end, then you don't know too much about how a story is usually structured.