The following taken from above lesson is incorrect English grammar using the article "an". It should be "a" past action.
Il a fait froid hier soir. Here, I'm referring to an past action that has a clear timeframe in the past, insisting on it being a single, whole past event.
Here Le Passé Composé is used to express a sudden action that interrupts or "cuts" an ongoing action, a habit or repeated action in L'Imparfait.
Il faisait froid hier soir. Here, I'm stating that it was cold during the night, insisting on the fact that this situation was ongoing then, describing the situation.
It was cold last night.
Il a fait froid hier soir. Here, I'm referring to an past action that has a clear timeframe in the past, insisting on it being a single, whole past event.
It was cold last night.
