I would concur with what he said, I would associate drying agent with something like MgSO4 which is used to do what it says on the tin really... mop up the excess water in the vessel. Whereas a dehydrating agent I would say is on a more molecular level to remove water from a molecule.
Just be a bit careful about the phrase "removing water from a molecule".
It can mean just that, i.e. removing water molecules from other compounds (e.g. dehydration of hydrated copper(II) sulphate), but usually means "removing the elements of water from a molecule". It is usually one hydrogen from one atom and an OH group from another nearby location.
Drying agents bring about a physical change with no change in the composition of the compound whereas a dehydrating agent brings about a chemical change and a change in the composition of the compound.
Drying agents bring about a physical change with no change in the composition of the compound whereas a dehydrating agent brings about a chemical change and a change in the composition of the compound.