There was no discussion on set about whether Draco knows for sure if this is Harry. My opinion is that he knows exactly who it is. So why doesn’t he say so? The reason, it seems to me, is that the boy who had no choice finally gets one. He can choose to identify Harry, or he can choose to do the right thing. At every moment up until then, he’d have dobbed Harry in. Finally, though, he understands what Dumbledore told Harry early in the story: that it’s our choices, not our abilities, that show us what we truly are.
