Well, an A319 seats 128 people, so for each second the flight is late you are delaying the passengers by two minutes in aggregate. And that's not even counting any potential impact on the aircraft's next flight. So perhaps the FA was acting out of concern for the passengers.
Otherwise, I would imagine the incentives are actually reversed, meaning the FAs get paid for as long as the aircraft door is closed, i.e., more delay = more pay. Based on your other observations, it sounds like you just had a good FA who wanted everything to be on time.