It takes time for the line of passengers in the aisle to start moving. Just like a normal deboarding.
So these folks likely grabbed their bags while they were waiting for their chance to move. No delay caused.
It's not just the time it takes to grab the bags, it's the additional obstruction the stuff causes when trying to get a lot of people out the exits in a hurry. Have you seen some of the stuff people bring on board?! You really want that coming down the slides with you?