Absolutely. The reason is that, the network hashrate is purely an estimation, based on the time that it took to find the last X blocks and their relative difficulty over that period.

In a similar sense, the pool hashrate is also just an estimation, since it is simply adding up the number of shares that it receives from miners over a certain period, and their relative share difficulty.

If you throw 100 KH/s at the pool right now, the pool stats will quickly update due to the massive influx of shares, while the network hashrate will take a good while longer to reflect the added hashrate, as the necessary sample data is much larger and the estimation takes much longer to settle after a drastic change.

Not sure I was able to come up with a half-decent description on this... Well, I tried