This is a common "gotcha" comment from people who don't understand LLMs very well. Occasionally if you ask Gemini it'll say this as well. It has everything to do with the fact that ChatGPT is the most talked about AI model rather than data being trained on it
When Gemini had its 'identity crisis,' mostly in 2023 (whatever they called it back then), it looked like a pre-training phenomenon, explainable by mentions in the available corpus. The consistency here, and exact and persistent match to how ChatGPT would answer identical queries, suggest training on Q&A pairs from ChatGPT transcripts, presumably at the post-training stage.
