I think that the Tweet was totally unacceptable, racist and wrong. However, I also believe that it may have been made with honest, if completely misguided, intentions. That doesn't make it acceptable, of course, and I hope that the person that made the Tweet is given the opportunity to undergo training to understand why it's wrong. I hope that the person making this mistake wasn't just fired as some have suggested though. Just firing someone doesn't resolve the problem. Helping people learn and understand is what changes the world for the better?
A better way to improve diversity and understanding would have been for YouTube to share and promote videos discussing Black History Month and surrounding topics, rather than just to tell people to subscribe to creators because of the colour of their skin as this Tweet did....!