Bitcoin cash, as well as other Altcoins will move approximately in the same direction as Bitcoin. But the bitcoin cache has a closer connection, and overflow from bitcoin to bitcoin cache is possible.
I would not completely agree with this statement of yours, I don’t think altcoins has ever moved approximately in the same direction, when bitcoin is the dominance, altcoins usually decline so much in value, but the only time that altcoins do surge is when bitcoin becomes stable temporarily, it usually does not move while altcoins increase then.
Most of the altcoins that we see increase right now are just the top coins, and they are being controlled directly by bitcoin movement, they increases when bitcoin increases and they decreases when bitcoin decreases, their connection still cannot be explained, but these few coins increasing cannot completely be the judge for the rest. So if we think because the few top coins are increasing, alts are increasing, kindly check alts below the top 100 and see their performance.