Coding interviews are stupid (ish)

No need to be excessively polite in situations like these. A roll of the eyes, followed by some variant of: "Sorry, but is a bullshit question. I'm going to have to end the call / get going" is probably the most suitable response. Doesn't matter who's asking, how famous they are or what they've accomplished.

To be clear - negative bases have not only no known mathematical relevance, but essentially no mention in the literature outside of puzzle problems constructed specifically around them.

You're a programmer/engineer after all - not a dancing monkey.