It would be great to see that chart overplayed onto the price chart to see which one moves ahead (so to speak). Price moved up earlier this year, causing more miners to come on board, so probably hash rate follows price?
it is one of the many factors but at a slower response rate (meaning it happens a while after the price went up already).
but i believe this particular spike in hashrate is due to Bitmain getting ready to release a new version of their ASIC miner with more efficiency hence a higher hashrate. they usually test these things out and there is always a spike like this.