Correction:
Why would Scott Adams say that his boss told him it was about race?
That is the assumption of this discussion.
To me, we're beyond whether his race was a factor in promotion - he by direct provided self description is probably not a good candidate. But I'll guess beyond that.
Maybe his boss wanted to keep him in his current position but needed a scapegoat to blame as a factor beyond both their control. Keep in mind this would have been more acceptable to suggest in 1970s/1980s than 2022.
Maybe Scott Adams is making this all up or taking a partial comment and constructing his own flawed narrative around it, or, in the very least, neglecting key context to fully understand it.
Again, I don't know what you want me to say here. I never brought up the origination of Dilbert nor understand where you are driving this discussion to.