No, because it's a new account only associated with this thing. Granted, access logs on HN could be used to crack the problem, but getting to those is non-trivial.

I'm guessing he is using HN over tor, as well.

Looking out for HN users (other than voidnull) that write about Internet privacy a lot will give some candidates.

I'm not sure about that. I mean, he can register with HN with just about any anonymous e-mail address, no money needs to change hands so as far as I can tell it's perfectly anonymous.

HN doesn't require an email at signup. You only need to give one if you want password recovery to work.