Hence his emphasis on not trusting it, which was right before the sentence you're quoting here.
I use a variety of LLMs.
In my experience to date, ChatGPT really is a sycophant. Claude can be moderately stubborn. Gemini is usually very stubborn, practically unmovable, unless you present new facts or make a rock solid counter-argument.
But it is a sycophant and will confirm your suspicions, whatever they are and regardless if they're true.