I don't know for sure yet. My dad was an attorney and he would say " Oh &*^$" after accidentally on purpose letting something slip in front of the jury. If he really wanted the jury to know something, sometimes that was the only way.
I dont think this was for the benefit of the jury. But i do think he wants to be able to battle with Nurmi over the issue of this particular witness remaining anonymous. Not quite fair considering he is online publicly announcing his part in the trial as a witness. So if Juan slips and says his name, and Nurmi makes a motion, they get to argue the merits again.