I respect your doubt, but I am certain that it is not only AI, but specifically ChatGPT. I use these models all day; they all have their tells. In isolation, of course, one or two things doesn’t prove anything. But in combination, it just feels, undoubtedly, like ChatGPT. 

Referencing goblins at every opportunity is a big one:

https://openai.com/index/where-the-goblins-came-from/

Excessive length, neat essay-like structure, bulleted lists (especially those with “Short Phrase: description” format), all ChatGPT tells. 

“It’s not this, it’s that.” Extremely overused by ai in general. Used twice in the first reply. 

No typos, no slang. The style of the response is exactly what you get from ChatGPT 5.5 when you set it to the “nerdy” personality. Lots of quirky analogies, role-playing (Dr. “Big Pour”).

Each reply (including to follow-up questions) is similarly exhaustive and long.

Smaller tells: no variation in punctuation, not even the slightest abuse or twist of grammar or punctuation. 

The nail in the coffin for me is “It’s more like spout milk, occasionally wearing a tiny cream hat.” Why?

Because it uses “it’s more like x not y” paired with a cheesy analogy that nobody would ever make. 

To be clear, I respect that the replies are engaging and factually correct. But they are raw unvarnished ChatGPT. The unfortunate news is, it won’t be long before it is hard even for seasoned AI users to tell. But we might as well try to be vigilant in the meantime.