What country do you live in?

It may very well be that the reason 'black' people in your country are 'behind' others is because of their socio-economic situations. Some classes of people within a society come from disadvantaged backgrounds, hence why they appear to be not as smart, when reality it has nothing to do with that, and everything to do with the situation they are raised and live in. Often this isn't their fault, but the 'white' peoples fault.

I can only give you an example of my own country. In Australia, the indigenous community is fairly 'behind' the rest, because of their history and mistreatment at the hand of the white British settlers. Their communities were destroyed, they suffered from racism, they were allowed to become dependant on alcohol, their children were stolen from them, all because of how they were treated by the British settlers.

And today they tend to be live in worst conditions compared to others communities.

Does this make them inferior and stupider than the rest? NO. It simply means they did not come from the same privileged background as the rest ('white'), it means they do worse than the rest because they live in worse conditions, because they don't have the same opportunities as anyone else, because they were treated as inferiors by the people who your friend thinks are 'superior'.

This is in no way meant to make 'white' people look bad, it simply reflects Australian history and explains why the indigenous community does worse generally than other communities.

Your friend really needs to get in touch with reality, may Allah guide him.