Atheism is indeed opposed both to deism and to theism. It's just that, when it's strictly defined as being different from theism, deism isn't really worth refuting. It becomes purely academic because deism was initially crafted to give naturalists everything they wanted--a universe operating without miracles. God only got the universe started and then lets the universe proceed entirely on natural grounds. That's how early-modern scientists and philosophers could claim to be religious, wearing deism as their fig leaf while religion was practically irrelevant to how they thought about the world.

Were God to end the universe prematurely or supernaturally, that would be in line with theism, not with deism.

There's a more secular version of deism these days, namely the simulation hypothesis or the view that our universe was cooked up in a lab in another universe. But again, this borders on theism because deism is an unstable position. The scientists in the other universe could easily choose to intervene in our universe or to end the experiment prematurely. The deist has to say the intelligent designer necessarily leaves Creation to evolve on its own. And that makes little sense, once the deist affirms that that designer is a person. Can't a person change his or her mind? If that's possible, deism is liable to turn into theism.

Of course, if the designer isn't a person but a force or a substance, deism turns into atheism.