Satanism (as organized by Anton LeVay) is an atheist ‘faith’, no belief in an existing God or devil.
The coloring books are a ‘spaghetti monster’ style attack on organized religion and as such not a ‘religious text’ of a faithful people.
Unlikely that they did not believe in Satan as their god. The “humanist” aspect was undoubtedly a ploy to suck in proselytes and atheists. Otherwise why the black magic rituals?
Those damned Pastafarians, again...