I'm guessing the professor is mostly talking about rural Californians from the central valley farms. He's probably never been outside of the state to a place like Iowa or North Dakota. In any case, it's an ignorant and idiotic thing to say. May as well say, "All black people are criminals" or "all white people are racists." It's just stupid to make a generalization about tens of millions of people. How the hell would he know? Pretty embarrassing and repugnant for a university professor to say something so ignorant, though.
I'll add that it's also ridiculous and repugnant to make generalizations about university professors based on one professor's statement.