I consider myself an anti-theist atheist. I too do not claim to know with certainty.
I have no problem with people speaking in general, vague terms of what they believe. For example, "I believe in a higher power." That's great - fine by me. I see no reason to believe in one, so we'll agree to disagree. But when they start adding more and more details "I believe in God who sacrificed Himself on Earth for us to remove the burden of sin from us, etc, etc." These are specific claims about something they don't know and can't possibly know. They are making these specific claims with no substantiation.
That's the point where I become anti-theist. That's the point where I rip their claims apart. When someone spouts BS they do not know and cannot verify, I call them on it. The extent of my beliefs are "I see no reason to believe in a God as no evidence has surfaced to support the existence of a God. I believe God probably does not exist."
When some theist makes a lot of specific claims about their God, trying to convince me and then saying it's all down to faith, I become a vehement anti-theist. Why should I buy into their BS if they're giving me no reason to and literally admitting they have no evidence, or using ****tily-constructed "arguments" like "If there was no proof, it wouldn't be faith!"? Exactly! We don't NEED faith.
I don't get specific about my beliefs because I admit I don't know. But I'm also heavily against those who claim to know, too. I have just as much trouble with an atheist claiming "There definitely is no God" as a theist claiming "There is a God". Both are equally irrational.