The distinction between GPT-4 and ChatGPT is blurry, as ChatGPT is a chat frontend for a GPT model, and you can use GPT-4 with ChatGPT. The parent probably means ChatGPT with GPT-4.
Typically when people say "ChatGPT" without specifying which specific model they refer to, they refer to gpt-3.5-turbo (in case of API - or in case of the web ui, they mean whatever model is its current web ui equivalent). But now OP says they meant GPT-4, so, sure.
Counterpoint: I don’t refer to 3.5 when I say ChatGPT. I pay for ChatGPT, and always use GPT-4. Which I believe every paying customer do.