The mistake was using ChatGPT as an "AI detector" or "plagiarism detector." Of course, in an era of super-fast AI-generated content, all that software soon becomes useless, anyway.

But this is like using a hammer when the correct tool is a saw. That's really the instructor's mistake.

And they should be disciplined; that's not intellectual rigor, it's gleefully seeking out reasons to punish, and getting hoist by his own petard.