The reason your estimated honor for the day doesn't equal your actual honor is because Blizz has to calculate diminishing returns each night before they award you your actual honor.  This is why you have to wait a day instead of getting your honor points instantly.  You get 10% less honor each time you kill the same person in the same day.  So even though it said you accumulated 6000 honor, a lot of that was from people that you killed more than once.  After diminishing returns are calculated in, the actual honor is less.