I am rarely on twitter (just reading financial macro discussions, for which twitter seems to be a center of excellence), so probably have skewed priors. That said, skimming this information I see nothing particularly bad in banning the account that posted screenshots of internal confidential discussions.

This has absolutely nothing to do with the freedom of speech. It is related to breaking the promise (made when joining any company as an employee) not to divulge confidential information. This is a restriction on the freedom of speech that one knowingly agrees to when joining the company.

If I knowingly posted sensitive internal discussions from my employer I would be kicked out. Or worse: if I worked in a hospital and shared some sensitive pictures I might be hit with heavy fines or spend time behind bars. My 2c.