"Characters" in any other context are also by definition not curious. They're not open-minded or thoughtful either. Characters in a book are not people, they don't have thoughts, they are whatever the author put on paper. Yet we still use these words to describe them, as if the characters' consciousness and motivations existed beyond the paper on which they're described. It becomes really hard to talk about these traits without using words like curiosity and thoughtfulness. No one thinks the characters in a fictional book are real people.