Forgive me, but I don't think the Caucasian male was being serious. Are you sure you properly caught the tone of the 'argument'? With respect, I might ask: Are you, wisdom25, kidding, seeing what kind of reaction you can get?
For example, the Caucasian male said something about 'we was in America first and how immigrants and minorities came to America taking over their land'? Come, come now, that cannot have been a serious conversation you overheard.
Also: 'We won the war, came to America first and we don't get credit for it so therefore we should have a White History Month.'
You know what I think happened? I think the white male was kidding (the alternative is somewhat more ominous) but the black male did not recognize this, mistakenly took his conversation partner seriously, and then the white guy, finding himself under something of a verbal assault and too proud to back down and just say ('Sorry man, I was just kidding, making a bad joke') and found himself having to defend a ridiculous position.
That kind of thing does happen. I think its a mistake to take the conversation seriously. It was obviously a baaaaaaad joke that got out of hand!