I assume it is indeed a historical reference. The year 1955 was double relevant to Borges:
He had been an anti-Peronist , so he welcomed the Revolución Libertadora of 16 September 1955. In fact, the Wikipedia about Borges notes:
According to [Borges biographer] Williamson, Borges shouted, "Viva la Patria", until his voice grew hoarse.