Not true. First, to make an animation doesn't take weeks or months.
And second, has happens with drawing or music or code, AI can't generate exactly what an artist or coder has in his mind. But it can generate a somewhat close and not viable stuff for final work result useful to brainstorm and as a draft or point to start to work on top, helping to speed up their job.
No, what is done there is giving screenshots of Rockstar games and asking the AI to slightly modify it to make them more realistic.
Doing it by hand, the artists achieved exactly what they wanted. If didn't have use the trailer screenshots as reference the AI wouldn't have shown such similarity in all the details.
Also, to make that process of making a game screenshot look more realistic and detailed (can easily be done wih somelike like Stable Diffusion XL) nowadays takes some seconds. It can't be done 30 or 60 times per second (on top of the work required by the console/PC to render the game and handle the gameplay), can't be applied in real time for gameplay