In all likelihood, it wasn't close, but you can't have an airplane land on a runway while another plane is on it. LAX usually uses separate runways for arrivals and departures, so it's probable that another plane was rolling out after its landing, and 6000 feet down the runway (think: a mile), but hadn't turned off in time.

I think it says a lot about the era we live in where the most stressful thing an airline passenger is likely to experience is a go around.