The news media here is ridiculous. One day, the controls cause the price to rise. On other days, they cause it to fall. The controls do not matter. It's how people react to them. If there are controls and people can buy dollars, they might be more incentivized to buy because of the controls. However, if there are controls and you don't have a peso to spend, it's clearly impossible to buy dollars, controls or no controls.
So, it's pure supply and demand.
My guess:
I believe the situation with the holdouts had a lot to do with it. I think there was a lot of fear that Argentina would have no choice but to pay, and that would imply a megadevaluation as it would open the flood gates to some $15 billion being paid at some point. With that possibility, there was probably a lot of speculation, and that speculation fueled demand to some extent, as well as the price that brokers published. If you're buying and selling dollars, the last thing you want to have is a ton of pesos on hand in an environment where the dollar reserves could fall 3 billion from one day to the next, and then 12 billion more after that (to pay those who accepted the canje de deuda).
But evidently, the price got too high for those to buy dollars. So, the price has to fall to incentivize those with pesos to buy dollars, and to disincentivize those with dollars from selling them.