Almost every exchange tied the altcoins to BTC, if their not tied to ETH. That's why if BTC goes down, all crypto tokens will go down too in terms of USD price as it was tied to BTC. It's like the Law of Relativity or it's like how a specific market/country crashes when their currency crashes in value too in FORex. It's like a common occurrence in the market. Wether it be stocks or the crypto market.
The exchanges may give you a value based on bitcoin, but that's not tying them together. Just because it tells you that 1 altcoin is worth x bitcoin doesn't mean that if one goes up the other has to go down. These exchanges have no impact on the price.
Forex is the same. A dollar is the same whether it's valued in terms of euro, franc, gold, corn, or donkey pelts. When a trader decides to buy one and sell the other, of course he will impact the price of both. But that is the decision of the trader, not the exchange.