A 6000' runway is plenty for an A320 even at MAX landing weight with tailwind, so runway conditions probably weren't a consideration. Auto brake commands a deceleration rate rather than a specific amount of braking, so if full reverse thrust is used little demand is made on the brakes once deceleration has commenced.
It's possible that they were practicing for more limiting runways, Captain showing a new F/O how quickly the aircraft could be stopped or the F/O practicing his short field technique in an environment were it wouldn't matter if he didn't quite get it right.