Naive bayes, with a relevant dataset, does a very fine job of data classification(sentiment analysis, spam detection...). Also, almost everyone who isn't a liberal arts major would have come across Bayes theorem in high school or college.
The question about A/B testing is solving simple linear equations. I believe anyone in 10th grade or above should be able to solve it.
Hashing and MAC are pretty much application level security - they don't require intrinsic knowledge of how; what and why is something an application developer should know.
That leaves us with that harmonic progression thingy and padding. Padding, I think, is to avoid cryptanalysis(extrapolating from what you know is a part of knowing things:)).
Overall, I won't say he is going overboard with his questions. If anything, to anyone familiar with the topics, his questions are pretty trivial. The only thing under contention is if the topics he considers relevant are actually relevant.