No, he didn't say that. He literally said he was a Confederate veteran, and that the climax is defeat of the "Yankees" (I assume he means that Alliance is the Yankees?) and that it was "offensive". Now, I assume that he is not completely ignorant and realizes that Firefly is set in the future and in space and other planets. But he still straight out states that Malcolm = Confederate veteran and Alliance = Yankees. Like the show had an agenda to promote Confederation and its values, or something. Even though it actually does the opposite as far as the Confederation "values" go.
If all he means is that Mal is based on the archetype of the hero who was on the losing side in a civil war, which is what everyone agrees on, what would be offensive about that? Please explain. Is there something inherently offensive about saying that the side that loses a war might not always be the worse one, or that people who were on a losing side in
a civil war might be good people? Or that the side that wins a war might not be all wonderful?
Or are you seriously saying that Firefly is really about the American Civil War and was made with an agenda to promote the Confederation and argue that it was all about freedom, that black people were equals to whites, and that there was no slavery in the South, but there was in the North?