Joel was a young boy who lived in Gotham City.
Joel was an acquaintance of Matt, Carrie and Nick. One night when the three were telling their own stories about how they viewed Batman, Joel (who was hanging outside the Shoemaker store) overheard them. He revealed that he believed Batman wears "tight rubber armor" and that his car can "drive up walls". The other kids dismissed these claims and walked on, noticing how a restaurant had fallen victim to an arsonist. Joel happened to be quite amazed with the fire.
Joel and his view of Batman are a jab at real-life film director Joel Schumacher, who directed both Batman Forever and Batman & Robin. The former of which indeed had a Batmobile that drove up the side of a building in one scene and was part of a series that did have Batman wearing rubber armor.