That is what you did:
You're wrong, grouping them all together is exactly what you did. You're saying that they're claiming to be British on one hand, while claiming a different status on the other. Name them. Who has said that exactly?
You're lumping everyone into one group, which is shameful. You're saying that just because some black people have a problem with the history of Britain, no other black people can say they're as British as you.
Seriously, how can you be so stupid to think "but blacks can't keep claiming" as if...
I've no problem with him turning it down on principle, although I can't say it his reason makes sense to me. Why would his ancestors be turning in their graves? If they were going to do that, wouldn't they have been turning when he ancestors moved to Britain for work? Haven't we moved on...