No. Gnosticism is not about whether or not you do know. It's about whether or not you can know. Agnostics make the claim that you can't know. Which is absurd, because if there was a god interacting with us, we'd know it. All the people who claim to feel god in their emotional experiences, they claim to know. People talk about their "personal relationship" with their god. They claim to know. A lot of gnostic theists fall back on agnosticism when confronted with criticism, and a lot of gnostic atheists fall back on agnosticism when trying to be completely accurate and not fall into some kind of semantic trap. Sure, we can't prove that no gods of any kind exist. But we can prove that Zeus doesn't exist. We went up Mt. Olympus and he wasn't there. We can prove that the Aztec god Tonatiuh doesn't exist, because the sacrifices stopped and the sun kept shining. We can prove that the god of the bible doesn't exist, because the world isn't a few thousand years old, and because dinosaurs and evolution are real. Also because natural disasters don't happen in correlation to "sinful" behavior, and praying for someone to get over an illness doesn't make a difference. These are all attributes of that god and when you strip away the attributes, there's no god left, just a nebulous concept. The moment a god is claimed to have done something, we can check and see if a god did it, or if it just happened naturally.
We are all very gnostic about a lot of gods. We are only agnostic about the possibility of the concept of gods.
And, of course, because this question always follows, "why do you atheists care so much about what people believe?" We don't. We care what people do because of their beliefs, and since beliefs invoke an appeal to an authority instead of rational debate to support them, our only recourse to stop the terrible things people do because of their beliefs is to dispel the beliefs.
