What does it have to do with ethnicity? He said "mainland Chinese", which is a form of citizenship. I think that all sides would agree that a good fraction of people from Taiwan are ethnically Chinese. As far as I know, citizenship is not a protected class (outside of certain treaties).

As for it being a good idea... nope. I wouldn't put myself in a situation where the Chinese government calls my employer and politely asks them to reassign me to the Antarctic branch. It's not a democracy, normal citizens have no power, and expecting your coworkers to do so is putting them and yourself in danger.