Maybe the officers play dumb to make sure the person claming to have been on said run actually speaks intelligently about it. Perhaps someone who claims to have been on one but can't define it is someone who needs closer scrutiny.

On a same day turn at FRA two years ago, the agent at the passport control in FRA asked me as I was going back to the departure gate:

Agent: "Wie lange waren Sie in Deutschland?"
Me: "2-3 Stunden"
Agent: "Schade, Sie haetten laenger bleiben sollen." (While stamping my passport)