What did Dumbledore mean by this?

I was reading Harry Potter and the Sorcerer's Stone when, in chapter 17 when Harry wakes up in the hospital wing, Harry explains that he had found out about Nicolas Flamel. Then Dumbledore says something like "So you 'did' do that thing correctly." The "did" is supposed to be in italics. What did Dumbledore mean when he said that? I've re-read it and I don't see what they did correctly.