Based on what you write, he would likely have a case for illegal race or national origin based employment discrimination if he reported it to management and management refused or failed to take action, despite having the chance to do so. But if he quit without reporting it, or reported it then quit before mangement could do anything, there would likely be no case: management is not responsible for what other employees do or say unless management is made aware of the conduct, has a chance to take action, but then fails to take action. So if your brother never gave management a chance to do anything, they did nothing wrong.