Because I do not believe in the almighty influence of Twitter, I honestly don't understand why it would matter if one or a hundred Chinese spies worked for Twitter, because Twitter employees don't create Twitter content; users do. And I think Twitter content was recently declassified by former President Trump, so where is the danger? What is China's strategic benefit in learning these[1] things?
Twitter has controversial moderation policies. It also has some sort of machine-executed algorithm for selecting which tweets to show to each user, and in what order.
Both of these mechanisms could be used to promote or suppress specific topics/stories.
Many people, including a very large number of journalists, use Twitter as a news source.
Taken together, I can absolutely see why nation state actors would want to exert control over Twitter.
spies can find the irl identities of otherwise anonymous dissident accounts, for one. i've read stories about chinese students in the USA being confronted with their post history by govt agents despite impeccable opsec.
[1] https://en.wikipedia.org/wiki/List_of_most-liked_tweets