The strength of the USD is measure by the DXY (US Dollar Index) which is a measure of the USD against a basket of 6 currencies. This basket is weighted > 50% in the Euro and also includes the CAD, Swiiss Franc, GBP, Swedish Krona and Yen. So it would make sense that when the Euro drops the US dollar goes up. When the US dollar goes up, the (immediate) value of commodities in general would decrease.

I understand and agree this would be a short term phenomenon, but it exists nonetheless. The US dollar is inversely correlated to the Euro by design, so if the Euro is tanking so are commodities ... it's just the way it is.