Depends. I am a decent software dev by all the standards I can observe. Yet I don't know a lot about number theory. I know a ton about other fields like e.g. control theory. If I now interviewed a django dev and asked them about control theory or hardware registers, I wouldn't even ask them whether they know that, because the answer is not really relevant to their position. I might ask them just our of curiosity, but then I would not care so much if they don't know it, I would care about how they handle dealing with something they don't know.

If they go all optimus prime that would be a red flag. If they show curiosity a green one.