Do anyone knows why ChatGPT “talks” about GPT-3.5?

I was trying to ask ChatGPT some advice on how to engineer my prompts (maybe its futile, but nevermind, that is not the point), hit 'enter' and noticed that the response mentioned GPT-3.5 [1]. When trying to dig deeper ChatGPT wrote that <> In a "fresh" chat, any knowledge of GPT-3.5 is denied [2].

Maybe every once in a while, GPT gets fed with wikipedia? Maybe the ".5" came out at random? (actually just the "." token was random and the "5" followed) Is this considered an hallucination?

[1] https://chat.openai.com/share/630926a7-388d-4762-8ee2-6bce24b1c7e3 (note that i missed a final 'is' in my question)

[2] https://chat.openai.com/share/f9b9e6c1-89db-4295-83c4-af12972c3ef1

[3] https://en.wikipedia.org/wiki/GPT-3#GPT-3.5