In her essay, "Tone and Language in Historical Fiction" (reproduced in a volume of Yourcenar's essays translated by Walter Kaiser under the title of That Mighty Sculptor, Time - Noonday Press), Marguerite Yourcenar expresses some ambiguity in relation to this passage.
"Eight words refused to be written in Greek; they could have been written a bit more easily in Latin, a language which already underscores emotions as ours does. But in which language had I imagined that Hadrian, who was bilingual, was dictating his Memoirs to me? No doubt sometimes in Latin and sometimes in Greek - which gave me a certain freedom. Yet there are moments where, inadvertently, I caused him to speak the French of my day, and these eight words seem to me, as I reread them, to constitute such a moment. The reader will ask why I do not, then, remove them. Because the impression, if not the expression, seems authentic to me...it is right to let inexactitude play its part, and even to welcome the enrichments it may bring us. On condition, of course, that that part should be as small as possible."