The problem is I don’t know that, and I’m not convinced the author can know that either. Perhaps it influenced him in ways he is not aware.
My policy is I never let AI draft anything I write. It’s all my voice and my constructions. If I quote AI I will make that explicit. I do allow AI to review and complain about my work, but not to make any changes.
I don’t want anyone to be justified in questioning my authenticity the way I am justified in questioning the authenticity of this author.