If domain is expired at godaddy there are some factors that causes miscalculation.
1. since domain was expiring, there might be some traffic from other domainers and so, day*30 it might increase monthly traffic alot. Also if domain is expiring and doesn't have much value, some owners just offer it and if nobody buy, then they let them expire. But domainers were there and increase traffic.
2. previous owner might have bought some cheap TGP traffic or spam some boards. This happens if somebody is selling domain to increase it's value.
3. We don't know if they count bots, it they come, it might get monthly value +100 or so.
4. All domains got estimates, but barely any is parked at sucking cashparking (my sig offers better :D). They don't have HW resources to check all domains traffic. They probably just multiply first day of cashparking * 30. And imagine +100 monthly by bots as it might have been counted and multiplied by 30.
5. We know godaddy got cheap domains but they are quite fishy (locking domains upon spam report, and many other stuff).
I find ex-TDNAM very good opportunity for godaddy to make nice cash from expired ones so why wouldn't they increase the traffic to get higher bids? Anybody will do this.