A professional florist generally conceals all mechanics of any design piece (this includes wire, green foam, plastic cages, etc.) She is gluing artificial leaves to the underside of the bouquet holder with floral adhesive.
Floral adhesive is slower to dry than hot or cool melt glue, but holds better under moist or cool conditions. (Such as a flower cooler or home refrigerator).
Press firmly and make sure the leaves are firmly attached before handling the holder.
She snips stems off the artificial leaves and glues them one at a time, overlapping the leaf edges.
You can see she takes a few moments to make sure all the leaves are firmly adhered before moving on to the next step.