I'm a former Law student.
Not sure what format your college had for interviews, but my college had applicants read case extracts, and one of them was on contract law. We were asked some questions about the case (e.g. who did the judges decide in favour of? Why did they decide in favour of X?), and given various fact patterns to apply the legal principles in said case (e.g. I offer to buy your car for $X. You counter-offer to sell it for $Y. Is there a contract? Why or why not?). The tutors then modify the fact patterns to see if candidates can problem solve (e.g. I offer to buy your car for $X. You say you'll think about it. Two hours later you slip a note under my door saying "I agree to sell you my car for $X").
I didn't actually have to know anything about that particular case or even general contract law principles - in fact I had zero substantive legal knowledge when I interviewed and I had not read any of the cases I was interviewed on previously (I had to do three interviews because I bombed my second one, and the cases were from three completely different areas of law). The substantive knowledge itself can be taught (or self-learnt), so the tutors are mostly interested to see how quickly one can absorb and apply information. Everything that I needed to know to answer the questions could be found in the case extract itself, and it was just a question of understanding and applying. This is intended to be an approximation of a tutorial, where you will be presented with new information/ views and forced to reconsider/ refine/ defend your stance continually.
This is pretty spot on - I actually asked my tutors about this years ago and they are very careful to select areas of law which are more accessible and intelligible to laymen for interviews. Contract law makes sense in an interview setting to me because it's something that most people can relate to and the basics are fairly straightforward (as compared to something like Trusts, which I found to be mind-bogglingly hard at times).