I figured it might be a joke but it's a pretty common statement made in all seriousness so I figured I might as well...
The part that doesn't add up is expecting it to add up.
Just so happens I just got done publishing this:
Grass Fed Versus Grain Fed Beef: Fatty Acid Profiles, Antioxidant Content and Taste
BTW, hardly any beef cattle gets an exclusive grain (or corn) diet. That's a frequent misunderstanding. It's "grain finished" rather than grass finished.
Another btw, if you've never had it, grass fed beef tastes like shit.