Yeah that's absolutely correct. Bitcoin and Altcoin have a common relation and that is that they both are cryptocurrencies. So it is natural for them being relevant to each other. But it is not necessary all the time and it does not mean that if Bitcoin goes down then Altcoins will go down for sure.
It all depends on the market demand about a particular coin. 1 out of 10 times I have seen that the market of Bitcoin and Altcoin goes in opposite directions. The coin which has more demand is favorable on the positive side whereas the coins with low or no demand goes down.