Why didn't the board explain itself clearly?
There are times when saying anything publicly would be considered defamation and openining themselves to lawsuits, but it seems that they owe it to their own staff in plain words. They didn't explain the situation properly as per leaked internal announcements.
OpenAI is not a typical LLC or S/C-corp though, so the Board also has to overcome that conceptual hurdle.
I think you are right that Ilya didn't want to give out secret information to not open up himself to lawsuits.