I've conducted a lot of interviews (in an academic setting in the humanities), and I can say that it's risky guessing what exactly the interviewer is trying to accomplish with a question. Sometimes a question is asked neither to see if someone knows the answer to the question nor to see the content of the interviewee's answer, but to see how the person handles being asked such a question. I could see someone deliberately asking a question that he know the candidate not to know the answer to just for such a purpose, though personally I would avoid doing it as it's neither nice nor useful to stress out the interviewee even more (but I might do it in a mock interview preparing someone for a real interview).
So the interviewer might be interested to see if the interviewee honestly, humbly and politely says: "Would you like me to tell you the container classes I use the most? The others I have to look up when I need them", or if the person pretends to know the answer, or rudely bristles, or tries to weasel out of the question by changing the topic (of course it might be a bonus if the interviewee actually has a great memory and knows all the container classes; but then another question might need to be asked to gauge character).