Damn. That does fill in the rest of the pieces.

[As he'd said, Izunia has never asked Prompto exactly what went down. That Noctis found Prompto chained in a cell had been enough to explain the boy's overall traumatic reaction to Ardyn, combined with everything else.]

I knew that he had some background of the sort, but I didn't realize that he was a clone of Verstael directly. Damn.