They didn't blow that amount, they spent that amount. But they received that amount of pesos back at the market price. Of course if the peso declines, as it almost certainly will, they will lose money, but they're not losing the total amount, just whatever percentage the peso declines.
Am I being invoked here? If so, I’d suggest that in a narrow, rather pedantic sense, you’re correct: there are now 1 billion Dollars worth of Pesos (rather less, since the Peso has continued losing value) sloshing around the Argentinian economy.
Did anyone want those Pesos? No. In fact, it’s a stated objective of the government (they make a lot of contradictory statements, I know) to “dry up” Peso liquidity. Adding billions more isn’t exactly going to help.
Is this where the increase in M2 money supply is coming from?
Then you have the impact on the exchange rate, adding billions of Pesos on one side, and having fewer Dollars to burn in defence of the Peso on the other side. That will worsen the exchange rate, in a vicious circle with each iteration of intervention. Perhaps ending up with something like Black Friday where the British and Irish pounds (then linked) were forced out of the ERM by speculators. Only this time it won’t be so nice.
So yes, considering the big picture, I think “blow” is the appropriate metaphor.
The only way out here is for Milei to accumulate a war chest sufficiently big to wage shock and awe on any speculation against the Peso. That’s why he’s trying to set up a currency swap with the US. Maybe it will come, but let’s be clear, there is no plan.