he usually posts both charts a BTC pair and a USD pair. But, he has said a few times he prefers using USD himself. It doesn't matter I think. From my understanding its the SAME price at the end... USD stays at 1.00
BTC fluctuates all day long. So USUALLY when BTC goes up the price of most coins will go down.... not always but usually.

But i would like to hear @haejin reply again too lol.
Just to understand it a little more