I can't find anywhere online that shows a picture or video of the cow in question in this show, unfortunately. Any way you could find one and share it here?
I can say, however, that dairy cows are intended to be much thinner in muscle and fat mass than other cattle. This is because they are bred for their excess nutrients go to milk production rather than weight gain. Little muscle/fat mass is not necessarily a bad thing, as long as it's not a reflection of poor nutrition or malnutrition. Just like a 15hh Arabian is not going to have the same muscle and fat mass as a 15hh gypsy vanner, but they could both still be excellent models of health and fitness for their respective breeds.
As highly emphasized by my livestock animal professor, who is a veterinarian and teaches animal welfare courses - a skinny dairy cow does not automatically mean underfed or poor nutrition. In fact, she gets concerned about dairy cows whose bones are not visible. But it's impossible to know without a photo or video reference, guess I'd have to hunt down the movie and watch it.