To clarify:
1. Gemini and Firefly are programmed (by a prompt) to give you "inclusive" results when you ask for depictions of people. So if you ask it to generate a crowd of people, while normally the AI could generate mostly or purely white crowd (perhaps because white people dominated the training dataset), with such a prompt it will try to give you people of both genders and all races.
2. Because of the above, in some context where you would expect only white people, for example the founding fathers of USA, it also depicts people of various races and genders. This is historically inaccurate and produces a lot of controversy, especially in times, when doing the reverse, depicting a historically non-white person as white, usually leads to some kind of outrage. And so such behavior is put to the same category as e.g. claiming "you can't be racist against white people".
3. And as a result, many people decide to "fight back" by trolling the creators of the tool, using the bias where instead of being negative towards white people, it is negative towards other people. So instead of taking positive figures like the founding fathers, you ask AI to generate depictions of evil people, who historically were white. Now the groups who claim "you can't be racist against white people" suddenly care about the historical inaccuracy. The trolls turn their enemies against each-other.
4. Your example with making the black nazis image manually misses an important point: the prompt used wasn't "a picture of black German soldiers in 1945". It was "a picture of German soldiers in 1945". If you ask an artist to draw you an artwork, which you describe as the latter, and he creates a picture of black soldiers, I think you just wouldn't pay and consider the contract to not be fulfilled.