there could be some who argue that it's not, that altcoin has it's own price movement. Maybe a tiny percentage though, specially those meme and shit coins who are being used for price manipulations, i.e. pump and dump scheme.
In my opinion as well, altcoins are not having their own way of price movement but they are simply following bitcoin market; an altcoin's market movement can be directly proportional to bitcoin or invertably proportional to bitcoin market but when there will be a significant chance in bitcoin market then that will reflect in all altcoin's market.
At the same time when a altcoin market is into high level of manipulation then it will be having completely different market movements from bitcoin because when manipulations are happening such altcoins will not have significant volume which helps them to be pumped or dumped at any extreme levels easily.