Jason creeped on the rooftops during one his nightly patrols. He had been lying low recently, since it seemed Batman was out of town and other vigilantes, including some oaf dressed as Batman, were handling the city. He still needed some time to prepare and this gaggle of vigilantes weren't helping.
And then there was this kid on the rooftops. Seemingly the same age as the kid he met just awhile back. And he was wearing some makeshift Robin costume. His costume. That was his tunic.
He swiftly ran and grappled across the rooftops, silently landing behind the child.