What counts as “plagiarism” depends on the context. It is (in most cases) unethical to present the work of another human being as your own, but what about an AI? In an educational setting, it would be unethical to turn in an AI’s work as your own. But if a professional programmer uses GitHub Copilot, are they obliged to acknowledge Copilot’s contribution? If I have a personal blog, and ChatGPT helps me write a post, am I obliged to acknowledge ChatGPT’s contribution?
I think the bigger picture to me is something like are you being disingenuous rather than are you technically plagiarizing. Thought experiment: if I tell people I’m great at multiplication and I don’t tell them I have an earpiece / mic with someone using a calculator on the other end. If I convince these people I have a great mind and they respect my math skills, have I not fooled them? As for the copilot argument, I’m not convinced it shouldn’t be required to cite.
Somewhat of an open question really. I think for all of blogging we have concluded that the words in your blog post were in fact written by you. I see two reasons plagiarism is bad: both and injustice to whom wrote the original but also a false indicator to your cognitive and creative ability.