Atheism, from the Greek atheos (a-theos, without gods) and '-ism', denoting belief, means "belief without gods"
This can be either the active belief we are without gods, or the passive belief that simply omits them, both are atheism.
The claim that an atheist must be claiming to know that there is no god contradicts both the etymology of the term and its common usage, and as such is an ignoratio elenchi or red herring.
The argument that an atheist would have to have the attributes of a god (omniscience, omnipresence) in order to disprove a god, and hence is disproved by contradiction is sheer sophistry. Such an argument would apply to any claim to knowledge, hence since it is itself a claim to knowledge, would itself be disproved by contradiction.
For example, most people would be happy to claim to know the world is not flat, yet there is not a single proof it is anything but. No traveller's tales, no measurement, no photograph of our orb from space is proof of a round Earth, since to be so there would have to be no other possible explanations that explain that data and are compatible with a flat model. Are "round Earth" proponents claiming omniscience now, to know there are not?
To say you must be omniscient to be an atheist is to claim the same is true of someone who believes the Earth is round or the sky blue. It is an strawman epistemology supporting a strawman argument.
