sometimes bitcoin and altcoins move together, but you can be sure that if bitcoin has increased then altcoins will also experience it, what is usually done by speculators is when bitcoin is bullish and is considered to have reached its climax, they will look for potential altcoins to buy and have not experienced a significant increase, so they still have hope of getting profits according to their targets. things like that often happen during the bullish season and prove to be profitable
Generally, in a bullish market, all the cryptocurrencies tend to go up along with Bitcoin, they don't go down or stay stable when Bitcoin is going up, altcoins are following the trend, and as soon as Bitcoin stops going up, altcoins also stop right there, and then move again when Bitcoin does. Sometimes, when the market is in normal conditions, like no bull no bear, some altcoins tend to move in the opposite direction from Bitcoin, if it's going up, they go down, and vice versa.
But this doesn't happen very often and not with every single cryptocurrency, it only happens sometimes with only a single or a couple of cryptocurrencies, and it doesn't continue for long too, it starts doing this now and it might go up and come down a bunch of times, and then it starts following Bitcoin again.