that's a stretch. if the intent is to create a sarcastic nick-name that compares the ceo to a dictator, "chairman pao" is going to be a front-runner not because pao and mao are both chinese but because pao and mao are only 1 letter different from each other.
You can't really reason with people once they labeled something as "racist". Convincing them that they are wrong would imply that they can't differentiate between what's racist and what's not and that's something that would affect their core beliefs.
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