He probably couldn't wait any longer! Our Syrians have always waited till they get back to the nest to de pouch and snack, to keep the food safe, but if out of the cage for a while your hammy maybe couldn't wait any longer for his snack
In fact, as Cypher says, he must be very relaxed with you, because whenever ours have had full pouches they are usually very active and wanting to go back to the cage and won't settle.