I don't think he ever presents it as being "entirely about carbon." Here is the first sentence There is a movement of people who really want people to eat food that is produced locally. Their argument seems to be primarily about the environmental impacts of moving food long distances.
I think he has a point here. If you were to talk to a champion of the local food "movement" and ask them why it's important, I would guess this would be the first reason given. It's not the only drum they beat, but it's often the one that's beat on the loudest. -From my experience.
The first reason given would be environmental impact. The second reason given would be the local economy. the third reason given would be food security. And all of these reasons would be accompanied by attribution and further discussion. None of this "silly people, the thousand-mile caesar salad is good for CONSUMPTION! CONSUME CONSUME CONSUME!