Reasoning typical of the o1-mini model appearing in the 4o model?

Hello! I encountered an unusual situation while using ChatGPT, and I’m curious to understand what it might mean.

I was playing hangman with ChatGPT, guessing letters. At one point, the model unexpectedly offered me a choice between two responses, which surprised me because responses are usually sequential without any options. Additionally, one of the responses felt as though it was written by a different model, such as o1-mini or o1-preview, since the tone and reasoning seemed different from the usual ChatGPT interaction.

Does anyone have ideas on what could have caused this behavior? Could it have been an accidental model switch or some experimental feature being tested? Thanks in advance for any insights!