This is why Oxbridge admissions are a bit of a crap shoot.

What they're really after is whether you can keep thinking and not be intimidated into silence. Just about any subject that a professor understands can be taken to where a high school graduate is stumped. You can always add twists to just about anything interesting. They key is to realise they are testing whether you'll interact well, not whether you can figure out the answers.

I was quite fortunate, they kept asking me things that I knew and they weren't disappointed with where my limits were.

It does come off as a bit confrontational to the modern observer I'd say, and it does give the impression that tutorials are some sort of intellectual sparring match. They're not, clearly you'd be flattened by the professor if they were.