They have a very confusing admissions process, but I don't think that admissions to the joint program are related to admissions to the Booth Economics program. I've heard that applicants to the joint program can be rejected by the Econ department and admitted to the Booth Finance program (and vice-versa), that's why I think it has nothing to do with Booth Economics. I could be wrong, of course.
PS: I'm also waiting to hear from them (Booth Economics).