No one was excluded from the Trump event. Same for Bernie Sanders. African Americans decided on their own whether to come to the political rallies of stay away. No one excluded them. Perhaps they self-excluded but Chris Matthews was lying when he said Trumps rally excluded African Americans and Matthews knows better.
Whether or not African Americans come or stay away is up to them but for Chris Matthews to ask how many African Americans came to a Trump Rally is to hint and wink that they were kept away.