I think Argentina did some things well, such as the early strict quarantine and social distancing. However, I don't think the BCG vaccination has much to do with it. For example, France and South Korea both have mandatory BCG vaccination and they both have high infection rate. For South Korea, it was a systematic approach that helped contained it quick - social distancing, massive testing to identify the locations of the clusters, proper quarantine, and their culture of wearing masks and citizen cooperation. As for testing, I don't think the CV strain would have mutated that quickly as to make the WHO approved testing procedures obsolete. Many countries have used it with success, otherwise they wouldn't be using them.
Also, like many other countries, Argentina did not (and still not) do much testing for whatever reason, likely because of budget. And like many other countries, I'm sure they under-report. Can't report what you don't test. Same goes with the number of reported CV19 deaths. If you don't test the dead, then how do you know? Best way is to visit a few hospitals and see if they're in crisis or not. News are not reporting hospital overloads like NYC or dead bodies waiting to be picked up roadside in Ecuador, so I'm sure Argentina is still pretty safe.