I don't see how a US company, the NBA, feels as if this is so much of a threat that they're willing to let look the other way on people getting LITERALLY killed in the streets due to fighting for their freedom.
But if you read a little bit more, you find the reason into why he did this.
Check it out: https://www.wsj.com/articles/lebron-james-says-tweet-supporting-hong-kong-protests-was-misinformed-11571107697?mod=hp_lead_pos9
Seems normal to make statements like this one.
Nike has a lot of profits from the products that are produced in the Chinese soil so they need to keep the bonds between US and China strong. And in order to do so, athletes like Lebron James is a great tool.