Very interesting article. I agree that when cows are raised in a humane way on a pasture, that they are a more environmentally friendly source of food than grains and wheat. However, in the US at least, 50% of all our grains go to feed farm animals. Which means that this massive environmental impact of growing those grains is used in large part to feed the meat we eat.
What I find interesting, though, is that the article assumes that grains are the primary source of a vegetarian diet. As a vegetarian, I try to avoid grains in general, preferring fruits, vegetables, nuts, seeds, and legumes, all of which (especially fruit) are better for the environment than grains.
Environmentally, fruit is by far the best food you can eat. Because fruit comes from plants that are not destroyed when harvested, growing and eating it is actually better for the environment than not having planted it at all. And I'm pretty sure all of us, vegetarians and meat eaters alike, could use more fruit in our diets!