Im confused too why this things happen 
, if I remember last year when BTC pump altcoin dumps and when BTC dump altcoin pump , but right now there are moving in the same trend if BTC dump altcoin dump much more .
This question bothers me too. What i have noticed is when the price of bitcoin goes up , the price of altcoin goes down and when the price of bitcoin goes down the price of altcoin goes up. So i think its invesely proportional to the price of bitcoin. But sometimes the prices go oppposite. So there is no fixed equation to the proportionality of their prices., if I remember last year when BTC pump altcoin dumps and when BTC dump altcoin pump , but right now there are moving in the same trend if BTC dump altcoin dump much more .