I've been watching charts for the past couple of hours and BTC price reached ATH but ETH price doesn't even moved. Suddenly BTC price dropped and ETH price dropped as well. Why doesn't go up with the price increase of BTC?

As I expected, if you want to exchange crypto to crypto, BTC <-> ETH, if the price of BTC goes down, the price of ETH goes up and if the BTC goes up, the ETH goes down. But why the fiat to crypto value doesn't goes change as well?