Maybe he recognized the voice, assuming it was not disguised by a charm?
Well, as he said, it was an "obviously hidden" horcrux screaming "I'm apowerful magical artifact" (like the locket in book 6, which he explicitly calls out), as opposed to a random pebble in the middle of the desert.
Well, I read canon a loooong time ago but IIRC in book 7 in one of the first chapter Voldie goes around humiliating Lucius, in particular taking his wand without offering a replacement, and insulting him for believing he (Voldie) would give Lucius his wand in exchange. The conversation with Mr. White (" most delinquent of my servants") and the fact that he humiliates him similarly by removing part of his magic ability is reminiscent of that.
Also, before I thought Mr. Grim was Peter Pettigrew, but now that we know that Black is the actual bad guy, it's even clearer that Mr. Grim = Sirius Black. In particular, Voldie says to him "I was surprised to see you here tonight; you are more competent than I suspected", which in retrospect clearly means "I thought you were rotting in Azkaban".
Well, the Dark Mark was not THAT stupid. Also, it's the kind of clever thing you can only pull off when impersonating someone who is not that smart.
Well I guess eventually the right memories will come back to her. Although I guess Draco can't have been more than a few months old when she "died".
For what it's worth, I too thought Mr. White was Lucius before seeing everyone else convinced it was Counsel. It seemed more in line with canon, and "white" evokes Lucius's awesome white hair. On the other hand, Harry could be mistaken, and using codenames that seem to indicate who the person behind is when they in fact bear no relation sounds like a thing Voldie would do.
Except people are cruel and many of them would rather see criminals in Azkaban than living a relatively normal life. Although to be honest, making criminals chose between Azkaban and the last part of A Clockwork Orangeis pretty awful already in my opinion.
Ugh... That's such a painful read I had to stop in the middle. Seriously, how is it rational for Harry to be insulting V in English? Even if V somehow does not take offense, one of his Death Eaters will. I know I felt like Adava Kadavra-ing the stupid brat who was pretending to be HJPEV in this...
How about "Unicorn Troll Jesus"?
Some long time ago he told Draco that Hermione was his enemy.