I guess some people just hear the words Muslim or Islam and think its all the same. It's not surprising though that a set of beliefs and black nationalism/separatism which espoused black superiority and distinctiveness would emerge out of American's racial history and prejudice. I agree with what you say about the NOI as an organisation but the same could be levelled against many other more mainstream religious institutions. It's a fascinating story how it all developed.
Plus Muhammad Ali was an ambassador of sorts when it came to negotiating for a hostage in a rogue nation, Ali was respected.
Ali spoke of it a lot. He said he did a lot of bad and wanted to make sure he did more good so he could go to paradise. When I mentioned Jimmy Swaggart Ali invited him to his home around the time of his initial Parkinson's diagnosis. The author suggested he might have had a crisis of faith and it rekindled an interest in the Christianity of his youth.