but also it is a common occurrence that when bitcoin price drops it takes everyone with it down. it happens every time!
However it the current market situation the opposite is also true, as BTC goes up against USD, ETH goes up against BTC. I.e. Ethereum seems to be behaving like leveraged Bitcoin.
it is also the size of the market and things that are going on.
bitcoin is much bigger and currently there is a lot of resistance because of all the negativity about it and all the panic sellers who are afraid which means price of it will go up slower.
meanwhile ethereum currently doesn't have that negativity and instead has a lot of advertising, specially using bitcoin's negativity which means it can go up much easier and less people are willing to sell it.
and also on top of it all, the rise of ETH with USD and BTC is because if you have looked at poloniex market when the drop was happening you could have seen manipulative buy walls be placed by the poloniex whales as big as 700
BTC to prevent the crash or at least slow it down. and that kept the price versus BTC up.