It is one of the best value holding coin and when other coins fall, people buy and store btc. Could be the recent fall of ETH, or any other.
It is not about other currency in my opinion I will say that. Why ETH fall just because they see the market of bitcoin that they are implementing people are afraid to invest. So, they have drop down there prices because they are not that much trusted as Bitcoin. But watch once again it is rising and rising so there would be no problem after 1 August or before as I'm watching the market.
I don't believe any other factor on bitcoin price effect. The only thing is rich people who can sell or buy hundreds of bitcoin in a minute on exchange web sites. This is the main cause for bitcoin price change.