Back when I first started hearing the "alt coins drop in price when BTC rises" stuff, it was after the first BTC pump. People would take money out of ALTs to put into BTC. A year after BTC reached it's first all time high, it was down around the 220 mark and stayed around that level (220-300 or so) for pretty much all of 2015. I think people learned their lesson that diversifying is a far better idea.
I have always found it interesting how BTC somewhat mimics the advancement of traditional currency, albeit at a much faster pace. It is almost similar to international currencies and their trade at this point in its own way. Ultimately BTC is such a central figure of all the cryptocurrencies that changes to it impact all the others, but if we have enough change in the others it could bounce back and impact BTC.