Well, they call themselves satanist instead of atheist to piss off mom and for the edgy aspect of that word, however that denomination is strangly accurate. From a Catholic point of view, refusing the surnatural world is indeed satanic. I'm not here to convince you by the way, only to explain the thesis so pls don't tip your fedoras at me.
In the Christian doctrines, two spheres exist and cohabit, the natural sphere and the surnatural sphere. The natural sphere is basically the human biological and intellectual fonctions, all the chimical and physical reactions. All phenomenons in the world for example react to the principle of causality. So man is, like all phenomenons around us, a natural person, the function of his bodies, his intellectual abilities etc. etc.
Based on that empirical observation, you can do two hypothesis to understand the origin of man and the world. The atheist one, who affirm that the nature originate in itself, have no divine origin, and the deist one, that affirm that the natural world is created by a God, that is himself in the natural sphere, it is the first cause, the supreme being of philosophers. Not a transcendent God, but a natural one, that created the laws of Nature and is himself in the natural sphere, as the first cause.
Now, from a Christian point of view, the natural sphere isn't sufficient in itself. That sphere indeed exist, but was a created by a God who isn't submitted to the laws of Nature, who exist independently of them, in the Surnatural sphere. More over, the man itself isn't only a natural creature, characterized by his body, by his natural intellectual and physical constitution and abilities. The love of god for humanity allows mankind to transcend the natural sphere and access to God, love, eternity through faith. The incarnation and sacrifice of Christ on earth basically sums up : The supreme being, in the surnatural sphere, who, enter the natural sphere, allowing mankind to transcend nature.