There’s a fundamental difference between the type of knowledge that 'knowing' is and the type of knowledge that 'not knowing' is.
The first relies on a posteriori claims. You cannot know that the largest mammals on Earth are blue whales unless scientists have observed it to be true. And — of course — there are problems with this type of knowledge. It’s known as the “Problem of Induction.”
The second type of knowledge simply acknowledges that our knowledge is limited. It doesn’t require evidence but it does rely on acknowledging that you can’t know everything, so it does depend on experience in a way.
So, at a fundamental level, equating the two types of knowledge is fallacious. They are completely different. The first one requires concrete, empirical evidence. The second one is justifiable.