Well IMO, he is ignorant on both counts. Any intelligent person knows a person's hair grows even after death...yes, that's right! So, how could he possibly think AA's hair can't grow once cut off?...that lacks both common sense and book sense. Also, he may have made the remark out of covert racism. Some whites feel they are not racist, but maintain very racist views about other ethnicities. I don't know this man so I refuse to pass any biased judgements or judgements out of hurt on him, but I think working under someone who has such beliefs would be uncomfortable for me.
I know not having a full understanding about another ethnicity is possible. For example, I once had a girlfriend, who is white, who ran a daycare out of her home. She came to me in tears one evening over something that had happened with one of the parents. Annie (my friend) had always believed that when AA's washed, some of their brown coloring came off. Well, she having two daughters would recall how their dead skin would come off, and thus believed since theirs came off in their skin tones, the same would be true of AA. Well operating under this notion, she went out and bought colored wash rags to clean up the AA kids after they played. Well, on this particular day, a mom noticed that she got white or light colored rags for the white kids, and dark colored rags for all the AA children when she cleaned then. The mom became angry and told her she was pulling her child out of her daycare because of her discriminatory practices. This mom went and called all the other AA moms and told them what she observed, they too came and got their children, some even leaving behind some choice words. Well, out of hurt and confusion Annie came to me. I told her that our skin color did not come off...and I even proceded to take a paper towel, dampen and soap it, and then run it across my arm to confirm what I had said. Annie cried for over 30 mins. in disbelief and embarrassment over her ignorance. I was not angry and I just hugged her. She honestly did not know, and she felt comfortable with our friendship to ask me. Well needless to say, the loss of so many children had an impact on her business, but she did get more AA children and used whatever wash rag she picked up to clean them.
In this case it was not actions or words done to hurt. I think your sis's boss wanted to try to "stick one to them" with his remark. But like I said, I don't know this man and I could be wrong. Your sis may just want to observe him a little more and then make a final decision about him.