Ollie wore that costume for a period before he died. I'm assuming Connor based his costume off of it as it was probably what Ollie was wearing when they met. I'm afraid I don't know the details as I only really follow Green Arrow when it overlaps with Green Lantern.
(Though I like the idea of CrazyPants!Hal continually referring to Connor as 'Ollie' and Connor humoring him. 'Yes, yes, Mr. Jordan, it's Ollie...you fascist.')