If you take satanist to mean somebody who worships Satan and Atheist to mean a Naturalist who thinks nothing Supernatural exists, yeah sure. But people sometimes use the words more broadly, so I said "most" to just avoid getting into a pedantic discussion about the distinction...but it seems I can't resist...
There may be some who call themselves both an Atheist and Satanist:
1) Somebody who thinks God exists but just hates God and worships Satan and considers themselves an Atheist because to them the term means Anti-Theist or against God.
2) Somebody who does not believe in anything supernatural but who makes out that they are a "Satanist" to mess with people or to act out against God (yes people sometimes do even while holding the intellectual position that He doesn't exist) or get attention.
But I think it safe to say most who call themselves Atheists do not fall into one of these categories, since very few people are Satanists.
Atheists who are public school grads and have no notion about Latin roots.
The Romans called Christians atheists because they didn’t believe in the “gods” and one God without a physical body was an absurdity.