I don't know enough to say that he doesn't use an LLM during his writing process, but I do know that I haven't noticed any appreciable difference between his newer videos and ones that were released before ChatGPT was made available.
Is it possible that this is just the way he chooses to write his scripts that you interpret as sounding like they are written by an LLM?
The only way to be sure would be to ask him directly, but some parts of the video set off my GPT radar _hard_. I tried to find them now by watching random segments but all of the ones I did were fine. It was probably inaccurate for me to say "sheer amount" or "clearly", but that's the impression I was left with after the video.
To clarify: I don't think he even took any information from an AI, it's just the style of the script that's iffy.
Some parts felt like those videos littering YouTube Shorts: https://youtube.com/shorts/NKUecaS69uk. Can you tell this is AI?