Light travels faster than sound would be my guess. The Blue Angels used to do their u-turn for NASCAR over my neighborhood and the planes would just zip by so fast, completely silent, then the sound would come, booming, then rolling behind them.
Edit: My husband says the lightning stretches over a larger distance than you can see from one perspective, so you're getting the extended sound from the extended flash. The light travels a couple miles in a flash, but a couple miles worth of sound rolls at you slower.
Upvote for the shout-out to Food Lion lol