your manager should not be evaluating another employee in front of you; it's a private matter between him and that employee.
When he vented to you, he was brandishing his power because he was not convinced that you respect his authority, or he was trying to test your ethical bottomline by way of your reaction.
In an office, the boss is always right (unless he does something unethical or illegal.) Do not question or contradict him in front of others. Try to help build his position and do a good work to make him look good.
See people beyound their ethnicity; the "content of their character" should matter more. When a manager complains about another employee to you, smile and change the subject to work related matters.
Don't treat your job as your life; it's just a means so that you can build a good life for yourself and your family. No one on her deathbed wished she had spent more time in the office.
There'll always be mean spirited people around. They are motivated by power. They have little empathy, if any, toward others. Some of them even relish in seeing the negative effect of their power on others. That's part of the human condition. Knowing what it is helps.
Forcus on the good.