I think that is only because he got tired of the underclassmen snickering at his mis-matched pairs. To solve that problem, he merely eliminated the common denominator; thus, arriving at the simplest solution
I never understood the purpose of matching socks. Freaky rule, if you ask me - try finding a matching pair in your sock drawer on a cold winter morning when you're late for class/work.
My rule is: if it's hot outside, don't wear 'em, and use sandals instead. If it's cold, then who cares if they are mismatched?