Please mind while looking at this graph the algo was changed and the new one produces less hashrates. From about the begining of May 2017 the network hashrate is growing continuously and there was no miner optimisation within this period unless I missed something.
Correct. There was no miner optimisation applied to Feathercoin directly
The hash rate has been climbing due to the approaching block halving, as most miners who are in it for a quick buck will mine and then dump just after the halving. Other miners want to mine and hold because after the halving the coin becomes more rare.