Causing a legal shitstorm is most likely
not a sustainable way to get ahead at big corps.
If this is what happened, I suspect Microsoft will drop this person even quicker than a hot potato, and even quicker than if they told them to rewrite it from scratch but the person took a few shortcuts too many (which would be my guess).
If they wanted to fork it, they could - just keep the attribution and be done with it. The fact that they tried to rewrite it suggests that someone wanted it to be legally not a copy.