No thats that not true  .  based on what ive notice when btc rise , altcoin also rises but not too much  . same as when btc falls   but there were also times that altcoin and btc are going independent or they are moving on their own way . 

Until now i dont really know the reason on why it is happening because what i know is that btc value is based on usd or any other local currencies and we also used fiats when we buy btc  but in the case of eth , we only use btc and the value of eth is also measured in btc