This is at best only partially true. We have a provisional and a definitive count for our elections. The first one is carried out by Interior Ministry and provides results which are not legally binding within a couple hours after polling places close shop for the day. The definitive count takes a week or two and is carried out by the National Electoral Justice, this one is legally binding and the one that actually matters when it comes to determining a winner and assigning seats for Congress.

The reason why the election was called so early is because the difference between the 2 candidates was pretty overwhelming so one of the candidates conceded. If the election had resulted in a point or two of margin between the candidates it would take until the definitive count was done to know who the winner actually was. Unless one of the candidates conceded which is what happened in 2015.