Where did you find the relationship of the dollar and bitcoins? The only connection is the cryptocurrency rate itself. The course is affected only by Bitcoin capitalization.
Thats right . btc is generally measured in usd , thats why they have a relation . if usd drops , btc also drops because people loose some cash .
Lets not forget that btc can be also measured in other local currency depending on what wallets you are using but then again , every local currency are always tied tup to usd because usd is still the general money .
Usd isnt highly volatile like cryptos . it can only decrease or increase a verry small increments . its not life threatening at all when usd drops .