I mean writers told him to say that Rock had his promos written in the wrist on Live tv?
You don't actually believe that was a shoot? It's The Rock. He could go out and do a 20 minute promo with his eyes closed. Rock's done ALOT of promos and he's never went to the ring with promo notes wrote on his wrist. It was a plan to get some fans on Cena's side.
Rock during that promo was trying to make the notes noticeable on camera. From stopping mid way and having a drink to him showing his hand to the camera. The whole promo was for Cena to get one over on Rock. The whole promo was set up for that one line.
The fans didn't fall for the notes on wrist at all. Cena tried making fun of it the next week and the fans didn't react and it was dropped.