Yeah... It's the symbol of the Church of Satan. Who just so happened to take the stereotypical 'evil upside-down pentagram with a goat head in it' for their symbol. Nobody 'messed up' by using it as a symbol for an evil, radical Satanist group. Calling the artist lazy for using it is an insult, and I call bullshit on it.
I mean, the Brotherhood of the Flesh is literally described in the first paragraph as a revival of medieval Satanism by insane people who, instead of acting rational, go out on debauchery and murder sprees for the fun of it. So no, it wasn't 'these guys are terrible, by the way they're Satanists,' it is 'these radical, extremist Satanists are terrible.' On top of that, they're all Awakened, with a powerful sponsor of some kind rewarding them for it (probably twisting them into more depraved acts with spirit pacts). Why would they care at all if they stole the symbols they used from a moderate group of some kind? It'd probably give them the giggles to cause problems with that.
There is no difference between Winternight's twisted Asatru and the Thuggees that are in the very same book from this Brotherhood of the Flesh besides that of origin and exact methodology. They're all insane groups using terror tactics and violence to achieve their goal (be it veneration of their deity, bringing around Ragnarok or getting their jollies/appeasing their sponsor).
So I stand by my point that nobody messed up.