That’s quite common. Before YouTube changed, there were thousands of videos showing groups of Black people beating up white people (in the US — I don’t know about other countries).
It’s also always the same in a one-on-one fight: as long as the Black guy was winning, all the Black folks would just stand around and laugh. If the white guy got knocked out, there was always somebody who would walk over and empty his pockets, maybe even give him one or two more punches if he woke up during the robbery. I saw dozens of videos with exactly this same script.
In case the white guy won, the Black guys around would make sure to jump in, either beating him up (and then robbing him), or in the best case, pulling him away to prevent any further damage to their brother.
This certainly has to do with the area they lived in and poverty, but it still seemed like Black guys are somehow more prone to this behavior than other races.