AOG - "/// To say that he 'had a problem' because ' you people used to be slaves ///
That is not quite what was said.
This is what was reported as having been said.
*** 'you have a problem because you guys used to be slaves'. ***
/// inferring that his behaviour towards her is because he is black and she is white, ///
That is completely your inference, colour was never mentioned."
Come on AOG, if a black person is in the conversation, and slavery is mentioned, are you seriously trying to say that this is not about ethnic origins?
" No difference to two white people quarrelling and one saying to the other "you have a problem because you guys are unintelligent idiots".
There is a world of difference. If one white man is saying to another '... you guys ...' then he pointing out a difference between them, although in your example that is not clear.
In this situation, the difference is entirely clear - I am unsure why you appear to be arguing that it is not clear.
" Now that surely is more insulting than stating the fact that "you guys used to be slaves"
Somehow I doubt it. Slavery in this conversation refers clearly to a specific group, of which the insulted man is a member - idiocy is international, and covers all racial and cultural boundaries.
" ... but even so, it would have been more correct to say "Some of you guys". "
No, it would have ben more correct not to bring race into the conversation at all - which brings us back to your question - yes, the woman was being racist.