Obi-Wan was glad to hear her being informal. It meant that very little had changed. Had things changed? Change was inevitable. Change argued that she was dead and that this meeting couldn't possibly happen. And yet there they were. The two of them. Far from the Clone Wars and the Empire that she never lived to see. He was glad for that.
And without even noticing it, his anxiety departed. Flew away as if on a breeze. And he was smiling. An honest and believing smile. She was there. As improbable as it was, she was there. Of course, simply thinking that this entire situation was improbable only brought a familiar (but always encouraging) voice to his mind.
Impossible nothing is, Master Obi-Wan. When trust in the guidance of the Force one has.