You could say that about almost any kind of knowledge-based evaluation.
If I ask somebody ten factual questions and they know the answers to five of them, how should I interpret that? Sure, it would be easy for me to just fill in those particular gaps in their knowledge. But assuming my questions were well-chosen, it's reasonable for me to expect that they'll continue to hit similar gaps in the future, about 50% of the time.
That's not to say that a good interview consists of drilling someone on facts; more often, they come up implicitly in the context of solving a problem. And as an interviewer, I'll look much more favorably on a candidate who recognizes what they don't know, because I give them the benefit of the doubt and assume that in a real-world situation, they would be able to do the necessary research. But even so, if there are basic things they don't understand, it's a red flag because it tells me they're encountering these concepts for the first time.
If I ask somebody ten factual questions and they know the answers to five of them, how should I interpret that? Sure, it would be easy for me to just fill in those particular gaps in their knowledge. But assuming my questions were well-chosen, it's reasonable for me to expect that they'll continue to hit similar gaps in the future, about 50% of the time.
That's not to say that a good interview consists of drilling someone on facts; more often, they come up implicitly in the context of solving a problem. And as an interviewer, I'll look much more favorably on a candidate who recognizes what they don't know, because I give them the benefit of the doubt and assume that in a real-world situation, they would be able to do the necessary research. But even so, if there are basic things they don't understand, it's a red flag because it tells me they're encountering these concepts for the first time.