Regardless of the intention, they ARE both chinese. So is it really a stretch to see a racist element to this nick name? It is racist by default. I'm not saying that it is a greatly offensive nickname or even unfunny, but for someone to call it racist is not at all a stretch.
but they aren't denigrating her because she is Chinese. They are denigrating her because they perceive her to be a terrible CEO, and Chairman Pao is a easy way to belittle what they see as her 'authoritarian' ways