The cover up is relatively easy for them, bearing in mind that nearly all international sites and sites showing tiananmen in the negative light are blocked to mainland china. And bearing in mind that the majority of their 1.6 billion people don't have access to the internet, those too young to remember won't really know about it except what passes on word-to-mouth.
And when your army is half nz's population, who cares what the rest of the world thinks, as long as you can manipulate your own history.