Just because bitcoin goes up in value doesn't mean all altcoins will go down. As of lately, it does seem like the majority of altcoins do lose some value when bitcoin rises but there are also some that goes up in value with bitcoin. If you're holding good altcoins, you should not worry about what bitcoin does.
What I think is the focus is on what altcoin he holds, and whether he has carefully studied the technology and team behind the coin. Instead of simply thinking that bitcoin will go up, we sell all altcoins. I do not think bitcoin will change much in the short term. If altcoin is large, then if the price goes up, it will make a huge profit.