From the end notes, I think the author's response would be that the carbon equivalent emissions come from the fossil fuel used in growing, fertilizing, harvesting, transporting, refrigerating, packaging, and so-on.
The larger point of the book is that specific accounting is messy, but if we proceed anyway we can get to the rough orders of magnitude that are more useful.
The larger point of the book is that specific accounting is messy, but if we proceed anyway we can get to the rough orders of magnitude that are more useful.