Network total 8.418 Thash/s
Blocks/hour 8.04 / 448 s
This information is referring to the last however many blocks found. In other words, it is subject to network variance or luck, just like pools are.
If miners are getting lucky and hitting more blocks than they would expect to, then Network total will appear higher. Its not like looking at poclbm and your hashrate is 300,000Khashes, and the Network total is just the sums of all of those on the network.
What I'm saying is, its possible 1 Thash was added, but its much more likely its simply the estimate is off because miners are getting lucky right now. That's why you're seeing network varying by 2 Thash, as opposed to 2 Thash of machines actually coming on or offline, etc. Not that there isn't people coming on or offline, just not as big a factor, I think.