Hahahahaha. I loved that call-out, but forgot to mention it. It was really surprising, hahaha.
It's complicated, but essentially it's the icon of a right wing movement against corruption, that strikes harshly against left-leaning politicians but is completely toothless against right-wing politicians.
"Pay the duck" is a weird expression (one I don't know the origins of) that means "Foot the bill for/deal with the consequences of the actions of a third party." In the context of the giant rubber duck, it was a way of criticizing the way the general Brazilian populace was footing the bill for widespread corruption by paying enormous and ever-increasing amounts of taxes.
But the giant rubber ducks themselves (there were many of them in protests across the country) were paid for by a completely partisan right-wing institution that wasn't really interested in fighting widespread corruption, instead focusing only on the corruption among left-leaning politicians as a way to kick them out of the way of right wing policy. Therefore, it fit perfectly with the capitalist flavor :P