If atheism is a world view, then everything ever defined that someone doesn't believe is as well. Not believing in Russell's Teapot is a "worldview", as is not believing in ghosts, as is not believing in push gravity, chemtrails, perpetual motion machines, bugblatter beasts and planet X.
A great deal will depend on precisely what it is that somebody believes doesn't exist, or has no ideas about at all, and on what implications the exclusion of that thing would have for other beliefs about the world.
God has historically been a central pillar in worldviews. The existence, nature and activity of God impact how people imagine the ontology of the universe, the direction, goal and meaning of history, how people should behave ethically, the goal of human life, and on and on.
Removing such an important pillar suggests that an atheist worldview is likely to look very different than the worldviews of most theists.
In other words, by expressing their lack of theistic belief, an atheist is simultaneously suggesting a host of more positive implications about the scope and parameters of how their own worldview is likely to fill out, about how their view of a Godless universe will look once the details are filled in.
The list of things that a person does not believe in is quite literally infinite.
Sure, the unknown is an open set.
But it's nevertheless true that not believing in things whose existence we may have no suspicion of and have no way of knowing about is still a big part of what defines the nature of our worldviews at any particular time.
Using the history of science as an example, the ancients held views about biology that didn't include what we know today about biochemistry, physiology, evolution and genomics. They held views about the larger universe weren't built around local heliocentrism, orbital mechanics, or any knowledge of what lies beyond our solar system. So doing the best they could in the circumstances, they advocated vitalistic biology, medical theory that involved balancing 'humors', and cosmologies filled with perfect circles, crystalline spheres and quintescence.
In other words, even the things that we know nothing about and consequently have no belief in one way or the other, can and sometimes do profoundly influence the nature, content and accuracy of the worldviews that omit them.