These spikes in hashrate are from people renting hashrate from Nicehash, usually to take advantage of merged mining income. As is often the case with Nicehash renters, this person seems to have had high DOA rates (~10%) during his hashing burst, which would subtract from his profitability. My guess is that the DOA rates this miner is getting are higher or equal to the revenue bonus he is getting from the merged mining, which means that he will probably stop after he has re-evaluated his profitability using experimental data instead of his predicted revenue.

If anyone is thinking of doing a Nicehash burst on p2pool, I suggest they let me know first. There are a few configuration changes they can make in order to improve their node performance, and there are also some code changes I've got on my to-do list that will improve fairness for miners with high vs. low hashrate and high vs. low latency.