The problem isn't the potential output of the land; it's that the costs go up rapidly. With a very large field a traditional tractor/plow/disk/seeder/cultivator can do a lot of work in a short amount of time. If the field is now 1/100 the size, the "tractor" (robot, etc.) and its implements don't cost 1/100 as much. They may only cost 1/5 as much, so your costs are now 20x what they would otherwise have been for the proportional output.
I think that's the point he was trying to make.