It’s not just about atheism in this, it’s about the gnosticism in combination.

Gnostic Theism = I am convinced by the claim there is a god. And I know my conviction is correct.

Agnostic theism = I’m convinced by the claim there is a god, but I don’t know if I’m right about that.

Agnostic atheism = I’m not convinced by the claim there is a god, and I don’t know if I’m right about that.

Gnostic atheism = I’m not convinced there is a god. And I know my (negative) conviction is correct.

Gnostic atheism is often also called positive, strong or hard atheism.

https://en.wikipedia.org/wiki/Negative_and_positive_atheism

I’m a strong atheist myself, following this reasoning:

The “no arguments argument” for atheism:

• (1) The absence of good reasons to believe that God exists is itself a good reason to believe that God does not exist.

• (2) There is no good reason to believe that God exists.

It follows from (1) and (2) that

• (3) There is good reason to believe that God does not exist.