They'd already potested the Argentine trade restrictions publicly. I'm sure they took a measured look at the best way to apply pressure to Argentina instead of rushing into it.
Don't forget that Brasil also backed Argentina (with others, obviously) on the Falklands statement, as a statement of solidarity against colonialism. And just as Argentina was implementing those restrictions...
Brasil backed Argentina with something they knew would make at least some of their important trading partners (North America, Europe) somewhat uncomfortable and they are repaid by Argentina implementing trade barriers that hurt Brasil, at least to an extent.
Brasil's not that happy with Argentina.
Neither is Paraguay, but that doesn't mean as much to Argentina for obvious reasons. Paraguay is impacted in many ways. They've sold agricultural products to Argentina, and in the last few years the beef exports from Paraguay to Argentina had gone up quite a bit in response to the Argentine government's beef export policies, which had damaged the meat industry in Argentina as farmers switched to easier to grow and lower overhead crops (to offest the increased restrictions), such as soy.
Beef prices rose significantly in Paraguay, as who wants to sell beef locally at a lower price than they can get exporting it to a beef-hungry country like Argentina. but it also provided a growth sector in Paraguay.
Now the story I get from my father-in-law in Paraguay is that a lot of exports that were being shipped to Argentina are not passing the border and there isn't as easy a market to jump to.