The best candidates light up when they have a chance to explain something cool, no matter who is listening and get even more excited when you ask a question about a detail. Good candidates are patient and thoughtful and ask YOU check-in questions ("so now we have X, right?") Mediocre candidates get a bit lost, sometimes overshoot or undershoot the right level of technical detail, but muddle through and sigh in relief at the end. Asshole candidates try to dump a bunch of smoke and mirrors on you, say shit like "well, if you haven't taken an algorithms class ...," wave off your questions, and pretend they don't have enough time to answer the question "seriously."
If you think in your engineering career you're never going to have to explain "how something works" in at least some detail to a semi- or non-technical person, you are not going to have much of an engineering career.