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?
Is there a devil behind every tree ?
YES
(And even if you don't believe that ... you should think and act like you do) ...
I think a lot of people would be surprised with their own thoughts if they would allow themselves the liberty to be paranoid
Anton LaVey claimed to have come from a Carny (carnival sideshow) tradition.
The black mass rituals and imagery were hucksterism. Made his orgies seem more “naughty”.