You can't really say Activision is so stupid in general, they removed most of the swastikas, but apparently they forgot ONE somewhere in the game, which is the reason the game is banned now.
According to German news sites which quote Activison Germany to the incident, it must be a rather inconspicious occurence of a questionable symbol, and even just for a very short moment in the game.
Activision Germany immediately stopped the game from being sold after finding out. As I am from Germany, this is another really sad incident... again...