I wouldn't say it was either of those things...the impression I got was that Athrun was just shocked at Rey. He had never heard him sling more then 3 to 5 words together in a sentence...and suddenly he starts talking about 'the past is the past.' I think he was just surprised that Rey was actually contributing to the conversation lolmonster wrote:And given what will happen next, Athrun is too nice, or he's too scared of Rey. He never seems to have anything to say to Rey.
But if we look at Rey's character from what he said...it is pretty clear that he has no real desires for the future. He is content with just sitting and letting himself be guided through the present by a certain someone...
He could complain that he is a different person than Rau...but it is too late, it is in the past. He is Rau and there is nothing he can do about it....talk about apathetic...