It is simple math really. Like having 6 / 3 = 2.
For example if Gold ( ) would be of value 6 and USD the value of 3 then XAU/USD equals to 6/3.
If USD devalues from 3 to a value of 2 then the equation becomes 6/2 and the outcome is 3. So when USD devalues the price of the pair goes up!
BTCUSD is a very volatile currency pair and I have placed a correlation index between BTCUSD and DXY below the chart. This allows you to roughly double check if BTC moves into the same direction as USD or opposite.
It just went into negative correlation with each other and with the NFP ahead and likely guaranteed volumes I am expecting USD to drop due to UJ and BTC to rally as a result of the USD events.