The cop should have invited the prof to sit down in his car and talk it over. That's what i would have done. I'd have said something like the following:
Sir, i'm not here because of your skin color, or my skin color, or the skin color of your neighbors cat. I'm here because somebody called me because you weren't entering your house as normal people do 99.9% of the time. If you had seen somebody you don't know "breaking in," wouldn't you call the cops? It'd be your civic duty to do that, you know.
I was concerned for your safety, and so i asked you about the other individuals. No, it's not my business who you have in your house, but as a police officer i want to make sure that you're safe, and that you are aware that there are others in your residence. What if i didn't ask you about the other men in your house, and just left, and then you, not knowing that you were being burglarized, went in and had harm come to you from those individuals? I asked you about the other people in your home, not to invade your privacy, but to ensure your safety. It's my job to determine whether you might be in harms way and to help you with that threat if it exists.
You have convinced me that you live here. If i can't convince you that i was just doing my job, and not doing my job because of your race, then i'll have to live with that. But you need to get about your business and i need to get about my business. There's nothing to get excited about as i was just doing what i've been trained to do, and what i would have done with a person who was white, black, or any other color. Could you please treat me as if i was your own skin color, so that we can get past this accusation?