when charlie visitis a college economics professor on may 15th, what does he discover that disappoints him? how true or accurate is this discovery?

By this point Charlie's intellect is far beyond his fellow students' at college. He sees an Economics professor but is disappointed when he lacks interest and knowledge,

"He explained apologetically, was outside his area of specialization. His interest was in interest rates, and he hadn't given military economics much thought."

This sometimes is the case with professors who have narrow knowledge about a subject and are disinterested in students.