I don't agree... Last few months we saw Ethereum difficulty increasing while the price was decreasing. I guess it's because new miners were starting with mining ETH and didn't care that the daily profit was decreasing. Only few days ago, when the ETH price was so low and difficulty so high that mining became unprofitable for a lot of miners, we saw difficulty decreasing.
I guess the team behind Ethereum decided to decrease the mining reward to fight inflation. I guess they realized that there is too much new ETH on the market every day. This way (in theory) the price should rise 33% because the reward will be decreased by 33%. But I'm sure the rise in price won't be that big.
I meant long-term