I was not expected to know how to calculate the static load on bridge segments like my engineer friends, but I was expended to learn the basic motion equations and be able to apply them. Equally, I did not take organic chemistry, though I had the option. I can balance an equation but not tell you what an "amine" or an "aldehyde" is.
My college's opinion, and one that meshed really well with my personal opinions on learning, was that you are better off having some surface level understanding so when you are asked to implement some sort of very complex algorithm about a domain specific problem, you will be better equipped to understand the domain expert and understand the common pitfalls that you should avoid.
My friend was a math major (and other majors) so he took number theory. I didn't totally understand all the things we talked about, but thanks to my understanding gathered from other higher level math classes like calculus and discrete math, he could dumb down his information a little less, and I could follow things like how it was funny when he was able to "prove" something on a test by doing every possibility, since there were only 24 possible outcomes, and why that displeased his professor.
If they go all optimus prime that would be a red flag. If they show curiosity a green one.
Asking the "what role does number theory play" question is a way to send a message and lose your chance at the job, but so does "optimus prime."