Atheistic Satanism?

[Reforged]

Most satanists are atheist. They are satanists as a mockery of their Christian upbringing.

Yes but Satanists are still in a sense religious. If you apply that kind of definition then technically we must call all who are religious atheists because to one degree or another they are atheist.
That isn't what most people do. What they tend to do is define someone by the religion they do follow as opposed to that which they don't. If someone follows Christianity you call them Christian despite the fact they are an atheist in regard to Islam.
Those who reject all religion in all its forms are defined purely as atheist in regard to all religion.

It does seem a valid question. Calling someone who follows no religion a Satanist just seems to be by its very definition a demonstrably false statement. They wouldn't call a Muslim or a Buddhist a Satanist. They seem to reserve this falsehood solely for Atheists.