Yes, it's exactly that. Most likely as she was a senior executive she'll have signed an NDA containing a "non-disparagement clause". That's the deal with the devil that you make in return for being paid $millions each year.
Doesn't prevent you from reporting to the authorities the flurry of illegal activity Twitter has likely engaged in. And if you're someone with ludicrous wealth... become a whistleblower and then fight NDA enforcability or pay the settlement if you have to. If you have any guts to put others over yourself and your terrible employer.
Edit: A few examples of these clauses: https://contracts.justia.com/contract-clauses/non-disparagem...