The offending image that FB chose to block a ~98,000-member group for was this:
So, nobody precisely knows what happened here. As far as I am aware, FB gave no official explanation and unbanned the group about 3 days later. The likeliest explanation I’ve heard is that it misinterpreted the image of the lead singer’s guitar as a firearm held in the hand of Creed-Dathon here.
I don’t envy Facebook the task of applying its TOS to images; that is, traditionally, the easiest way on Facebook to hide a TOS violation from auto-moderation (encode it in an image so text-based recognition misses it).
Part of me is suprised that a group with nearly 100,000 members doesn’t automatically trigger a manual pass before banning the entire group when the system detects a potentially violating image, but I don’t know the scale Facebook’s operating at; perhaps 100,000 is small-time from their point of view.