Self-analysis and self-interpretation is pretty clearly a key part of consciousness... I do wonder - how important to the process is the actual fidelity of the interpretation? Those people you meet who think they have deep insight into their own psyche while clearly having no clue... maybe they're p-zombies. ;)
So for the case of cats, I will understand cats at a different level from a cat biologist. I can point to features that seem catlike, and they can talk about all sorts of other scientific things that make a cat a cat.
With respect to that sciency kind of understanding, I don’t understand cats. With respect to a much looser ‘point at the features’ kind of understanding, I do understand cats.
While explanations are far from sufficient to instantly close the gap to expertise, they provide a massive boost that you might not otherwise have found on your own. The justification comes from the fact that their explanations are a reliable source of increased performance in making fine-grained distinctions. It's further demonstrated by answers to questions like "If they are so difficult to tell apart, why make these distinctions?" or "How did they come to be so similar?".
Do you understand cats? If I show you a picture of either a cat or a dog do you think you can tell which one it is? I think most people could solve that challenge, and if pressed they could vax poetically about what makes them think it is a cat. Maybe they would mention the shape of an ear, or talk about feline grace or what have you. But is that really a “justification”? Let alone one they can “defend”? How would “defending” even work in this situation?