That was how Douglas North, a Nobel laureate in Economics answered when asked about how his beliefs or belief systems can be quantitatively measured. He didn't pretend that he knows, he didn't speculate on a possible answer. He simply said, "I don't know. I don't have an answer to that."
He probably didn't want to lose time answering questions he doesn't have an answer too, when many more questions he can probably answer are on deck.
