Negative atheism says that lacking belief in God is the minimum requirement for being atheist. It does not claim that there is no God but that you just don't believe for you see no reason to. Positive atheism claims there is no God.
Lacking belief is not a conscious act. Denial is. If you deliberately, however, make sure you lack belief that is a form of denial. You are looking out for reasons not to believe. We will ignore that.
Negative atheism looks like it is confused for surely being atheist should mean you believe that God is not real? The answer is that as God is a claim about a loving benefactor, a creator who gives you all you have, then to oppose commitment to God is implicitly affirming that he is fiction. So negative atheism is denial but just not straight or blunt or direct denial. Silently saying "God is unreal" is atheism. Silence speaks. It is clear unspoken denial.
Let us reiterate.
You don't need to justify not believing. But if you make a direct claim that there is no God then you take responsibility for showing why your claim is correct. This does not apply to implicit claims but only to clear direct ones. The other may sense what we imply but that does not give them the right to tell us what we imply. Only we can do that. So there is only a burden of proof if you make a direct assertion.
Objectors say that just not believing does not amount to saying there is no God. Not believing in Argentina does not mean you are saying it does not exist.
But we have dealt with that. It expresses functional atheism and leads to deeper functional atheism. Functional atheism shows that you do deny God but not in the sense that you make a clear vocalisation that he is an untruth.
Also, we are all conditioned to want a higher power so lacking belief in God is denying God.
CONCLUSIONS
If lack of belief is a belief or leads to an implicit denial of God then negative atheism is believing there is no God in its own way. Lacking belief in God is minimalist atheism.