Barter is not a unheard of way to conduct business, even between countries without sanctions. The SWIFT network itself has become a sort of barter system.
I’m guessing in this case, they both distrust each other’s currency, so they might as well trade in Bitcoin as in any other currency they’d both trust more… if there was one.
Still, the USD losing that chunk of trade, weakens the USD, which the US might feel the need to strengthen with some “decisive action”.