Please don’t make the mistake of assuming that if you meet the minimum requirements for Oxford it’s enough for admission. That’s like expecting ivy admission in the US just because you got a 4.0 GPA. Like the ivies, they are inundated with excellent applicants- possibly a stronger overall pool than the ivies in fact, as British schools generally dissuade students they don’t think have real chances at acceptance from applying to Oxbridge (with a maximum of 5 unis on UCAS, wasting an application option is a bigger issue than in the US).
When I did my postgrad, I often used to breakfast with the lecturer at my college who did the undergrad interviews for maths and NatSci. I heard a lot of (anonymized of course) anecdotes during interview season… I would urge you to take twoin18’s advice about not being complacent about the interview seriously. Again: it is not about knowledge, it is about how you think.