The statement was certainly boneheaded, but when you visualize someone in the NFL being called a thug, do you visualize a white person or a black person? Are white players called dirty players or are they called thugs? If people answered honestly, I think they would likely visualize a thug being a black person coming from a ghetto environment and who had been involved in trouble while in school, maybe even gang activity, drugs, and weapons. Just my initial thought.
Well, the word "thug" often is preceded by "union" so I don't think thug by itself connotes anything racial. However, bad behavior by a black person should not automatically be labeled "thuggish". It's thuggish if it has elements of gangsta culture involved in the behavior. Things like excessive concern with "dissing" and a glorification of violence perhaps. I like Richard Sherman a lot. I think he was doing a little too much of a gangsta act on Crabtree, and he caught a lot of flak for it. That's not who he is, but a lot of people got a bad impression of him because of that one interview. Contrast that performance with the measured verbal smack he delivered in the press room after the game with the emphasis on me-di-o-cre. That sent the same message, but in a way that would not be labeled "thuggish".
He is right that thug should not be thrown around willy nilly at blacks, but wrong to ascribe racist connotations to those who did it with him for his post game antics. They just saw a screaming maniac and the word seemed to fit. Let it go.