Ah, right. Hard to see how Han could have gotten that figured out from mere Lassie barks. I mean, he could well get the "You were delivered to Jabba" bit figured out by himself while listening to Chewie's soothing but meaningless grunts, but he couldn't get Luke's name and the fact he's a Jedi now unless the growls really contained those bits of information.
Unless he got it out of Leia already and is merely ranting it out when paired with Chewbacca. Or unless the Force is strong with him or something.