the riots in Cardiff after the accident
Not much. It's still being investigated and is very fresh. I'd not call it much of a riot, more some neighbours kicking off on a rough housing estate in a poor area of Wales after the news of their deaths and a false rumour of a police chase had spread around the estate.. It escalated quickly but was resolved that night. Wales is not unknown for fiery tempers.
Did the two boys who died belong to some minority group?
No.
Were they really killed during the police chase?
No.
They were (probably illegally given their ages) riding something called 'e-bikes' without helmets. They had a tragic accident (not as far as I know involving another moving vehicle). The Welsh police have said that they were being followed. This appears to be confirmed by cctv on the estate. Doubtless they were riding recklessly due to seeing the police van.
How did you hear about it and why bother mentioning it? It's a long way from being the main news item over there.