In this situation, Gerry is engaging in Symbolic play. Symbolic play is the ability of a child to use objects to represent another object (i.e. Gerry using his cane as a fire hose). Symbolic play is not limited to just objects representing other objects. A child can also use actions and ideas to represent other action or idea.
At around pre-school age, (3-5) children become more creative and imaginative and are able to associate roles with certain actions like how Gerry says he is a fireman as he does the gesture of putting out fire.