I had dismissed flashback as too vague, but it might be correct. From the same site as the prior term whose definition I posted:

"Flashback

"A reference to an event which took place prior to the beginning of a story or play. In Ernest Hemingway's "The Snows of Kilamanjaro," the protagonist, Harry Street, has been injured on a hunt in Africa. Dying, his mind becomes preoccupied with incidents in his past. In a flashback Street remembers one of his wartime comrades dying painfully on barbed wire on a battlefield in Spain."

A problem with this term, though, is that the "flashback" episode in question is not defined as having relevanv=ce to the plot.

Shall keep searching.