Russia is a dwarf in the international economy. Putin is going to shake up the Bulgarians and force them to buy Australian gold to buy his oil?
If anything this behavior should be encouraged. Let Putin destroy the European economy when he tries to get them to pay in gold they don't have or can't afford.
To quote the article:
And of course, he still accepts US dollars as an intermediate means of payment. But he immediately exchanges all these dollars obtained from the sale of oil and gas for physical gold!