Kanji has grown up into a good man, and Jack's always felt proud that he helped, however slightly, to bring that about. It's enough to pull him some way out of the dark sulk he's been in ever since bumping into Ianto this morning and to turn his scowl into something at least approaching a smile.
"Hey, Kanji, what's new?" Look at him, making an effort! He's even gesturing to the next bar stool, inviting Kanji to join him.