The calories cows eat are ... useless to humans. We cannot digest cullulose (grass) and most of the rest of the things we feed to cows. Anyone throwing this number around has an agenda, and is not objective
Other crops that humans can digest can be produced on land currently used for grass.
Other animal species that eat grass require fewer feed cal per calorie produced.
In India, for instance, dairy cattle are fed almost exclusively on crop residues and by-products. Crop residues being what's left over in the field after you harvest and by-products being what would otherwise be waste left over after you process for human use.
Elsewhere, in addition to crop residues/by-products, you also have natural grasslands that aren't planted or irrigated, legume feed grown between major crop seasons when you can't grow anything else that also replenishes the soil and feed grown on otherwise marginal land or barely managed land.
Certainly some crops grown for cows would be edible by humans or the land repurposed for growing crops edible for people, but there's often a cost involved like heavier fertilizer requirements, pesticide use, water requirements, added infrastructure and/or labor.
Specifically, they can eat stuff that doesn't require constant fertiliser inputs, where as people-food generally does need a lot of fertiliser inputs and needs more intensive herbicide/pesticide application.
A balanced approach is to go, "Hmm, it's probably a good idea to raise cattle, chickens, and other animals, and also to grow all kinds of produce and staple crops as well."