Lack of belief is not a belief. I dont have to prove that there are no telepathic space weasels burrowing holes on venus and I dont have to prove that there is no God, the lack of proof is proof enough.
Though the interlocutor is no longer with us this gross error in logic should not be left uncorrected.
The argument above relies on a half-truth: the truth is - you cannot prove a negative, i.e. there is/are no god(s) and its counter-part of being able to disprove atheism. Both are equally absurd statements.
First of all, lack of belief is properly termed agnosticism, "without gnosis/knowledge." Atheism, by definition, is "without theism."
To claim to be an atheist is either to be a mislabeled agnostic or a declarative on the side of affirming no god. Personally I've found most agnostics are mislabeled atheists because they pretend an absence of a settled mind but really they are either atheists in hiding or they have some grudge against god they are trying to hide from...somebody...themselves or even god maybe.
But HJ says, "the lack of proof is proof enough."
Where to start...
First, it assumes there is no proof being offered. No person who ever sat on a jury ever saw the crime alleged but it would be a poor juror who insisted that unless he personally saw the crime it never happened.
Second, the statement is self-contradicting. He has to prove that no proof has ever been offered. The lack of proof that no proof has been offered means the thing he claims to refute would exist.
Third, the statement says that HJ himself is a reliable witness that has actually observed the evidence--or lack thereof--and that he is testifying truthfully and accurately to what he has seen or not seen. This is contingent upon HJ not having a conflict of interest, bias or hostility and that his faculties of apprehension and comprehension are sufficient. Judging by his post I would say he is not a reliable or impartial witness.
This is not to say atheism is non-existent therefore god must exist; I am only saying HJ is an inaccurate and unreliable advocate for atheism.