It's a chickenshirt rule that miraculously favored us rather than going against us as usually seems to be the case. They said there's a rule that in order to challenge and subsequently put time back on the clock (in a situation where the clock had run to 0:00) that there needs to have been at least 2 seconds left on the clock when they review the play.
Since the review only showed 0:01, we benefited from having to defend one fewer play than we would have had they been using rules that actually made sense.