In Carmack’s Facebook post, he talked about why he disagreed with the professor’s conclusion. Carmack emphasized that concepts and algorithms are not copyrightable. Rather, the law only protects a particular expression (or implementation) of a concept or algorithm. (I’m not an IP lawyer but that is my understanding of copyright law as well.)
Carmack argued that if you copy something and only change a few things or paraphrased it, it would still be a copyright infringement. But if you got the idea but found a different way to do the same idea, then that would not be infringement.
“The analogy that the expert gave to the jury was that if someone wrote a book that was basically Harry Potter with the names changed, it would still be copyright infringement. I agree; that is the literary equivalent of changing the variable names when you copy source code. However, if you abstract Harry Potter up a notch or two, you get Campbell’s Hero’s Journey, which also maps well onto Star Wars and hundreds of other stories. These are not copyright infringement.”
Anyway, Carmack argued that Oculus’ code was so far removed from Carmack’s code that the professor’s explanation for how the code was supposedly copied from Oculus was longer than the code itself. You can read Carmack’s comments yourself here.