What kind of jerk librarians are reporting stuff like this? And what kind of mechanism even exists for them to do so?
Once library fines get turned over to collection agencies, they appear on your record like any other debt. I have friends who work in libraries, and this generally happens after the library declares the book lost, as opposed to overdue, and charges you for the replacement cost of the book. If you don't pay, by the time it goes to collection, and the agency adds its fees and costs, it can add up.