Perón was close personal friends with Mussolini and Hitler, modeling his policies explicitly and in some detail on Mussolini's, and when he had to flee Argentina, he went to Franco's Spain. Mussolini and Hitler rose to power largely on their opposition to socialism, though they did of course attempt to co-opt its more popular policies (and in the case of Hitler even its name), and Franco's opponents in the Spanish Civil War were anarchists who were very explicitly extreme left wing. When Perón returned to Argentina, there were left-wing and right-wing factions of the Peronist Party, who immediately started killing each other --- like, literally at the airport when his plane came in. (This is not a literary invention by Garcia Márquez; it actually happened historically.) Perón sided with the right-wing factions.

Perón is hard to pin down: he adopted the most popular socialist policies with even greater enthusiasm than Hitler did. It's true that he welcomed fleeing Nazis, but he also welcomed fleeing Jews. The clearest aspect of his political alignment is that he was authoritarian and anti-elitist. But I think it's a clear mistake to identify him as a "left-wing populist".

As for the 19 teens, that's when Argentina was at its richest.

Gabriel Garcia Márquez is pro-capitalist. I said nothing about real socialism.