The airplane thing is not only in Argentina. I believe it happens in most intercontinental flights to/from LatinAmerica. My observation is that people fear they won't find enough place for their hand luggage in the overhead compartments. And honestly, in many intercontinental flights is the case these days, not only to LatinAmerica. Many of the passengers to/from LatinAmerica are families with lots of hand/checked luggage.
The boarding of certain rows is just very poorly organised and in my opinion it does not work, in any airport I have visited. Airline personnel are not very consequent with this procedure and only announce the procedure in two languages (usually the local language and English or the language of origin of the airline). Last time I was in Mexico, my Lufthansa flight was full of Polish/White Russian tourists who understood no Spanish, no English, no German. Accordingly they started boarding as soon as the personnel at the gate started announcing something, independently of the rows they had been assigned to. They were not really to be blamed. Airports don't have the proper infrastructure to make this ordered boarding possible.
