One important thing in higher education for math and physics is to be able to perform detail technical computations or modeling for phenomenons. In common high school and undergraduate physics class, it only requires students to be able to come up models with intuitions. But in graduate schools, you are trained to examine each step to make sure nothing is left out or based on assumptions that are wrong in your mind.
Therefore a lot of time you are not sure what something is until you re-examine all postulates that you learn when you are young.
An MIT-trained physicist should know the common name for a unit of energy. Sure, he might not remember the conversion from joules to calories, but to have never heard of it?
That's taking a literal reading ("I didn't know what a calorie was"), but perhaps he was referring to a more nuanced understanding ("I didn't understand how energy was used by the body"). That interpretation wasn't clear from the text though -- it seemed an overwrought attempt to portray an "Aw shucks, I didn't know what I was doing!" attitude.
"Calorie" in the context of nutrition has a different meaning than "calorie" in the context of physics. Three orders of magnitude different, to be precise. It's entirely plausible that he had no idea of the special nutritional definition, since you'd never encounter that outside of nutrition, and things like food labels almost always fail to make the difference clear.
One important thing in higher education for math and physics is to be able to perform detail technical computations or modeling for phenomenons. In common high school and undergraduate physics class, it only requires students to be able to come up models with intuitions. But in graduate schools, you are trained to examine each step to make sure nothing is left out or based on assumptions that are wrong in your mind.
Therefore a lot of time you are not sure what something is until you re-examine all postulates that you learn when you are young.