(I don't work at OpenAI so take it with a grain of salt) Yes and No they are similar. It is basically just a fancy autocomplete like llama, but I believe it's specifically been trained on chat content, or at least finetuned on such, and it probably uses a more chat focused labeling scheme on the training data as well to help it perform well on that specific task and be conversational.
So under the hoods, ChatGPT is just a model like Llama where they prepend every user input with a context that makes it behave like a chatbot?