I'd... really like to know how that's possible, since I couldn't have gotten my fin aid refund until the bill was paid.

You'd think that would be the way it works, since you're a logical person and that's the logical way things should happen, right? But you're forgetting that universities don't behave logically. I fully believe that they would have sent you a refund and then tell you that you still owed them money--mine actually did this. This semester. Of course, the amount I owed was way more than the refund they sent me, but I resented that they cut me a refund check and then demanded I give it AND MORE back to them. I know it wasn't personal but it sure felt like it.