czy to jakiś idiom?

After half an hour, he still hadn't appear, so he asked a young woman with blonde hair, who was also hanging around, if she had any idea where the pilot was. Then the penny dropped. "Oh no", said the woman, "Are you the reporter?", "Oh no", said my friend, "Are you the pilot?". The answer was "yes", to both questions. Co znaczy to penny dropped - coś w stylu, że zaświtało w głowie? ??