You stated you were arriving from Zurich. The officer asked you a destabilizing question: why do you have a Swiss debit card?
Such questions are meant to gauge your reaction and the consistency of your story. A legitimate holder would react, naturally, just as you did: “uh, because I said I live/study in Zurich, Switzerland.” A non-legitimate holder (one who is just repeating a story and not familiar with geography) might stammer, hem-and-haw, or try to talk the question away, like: “oh my brother is Swiss.”
This kind of non-sequitur probing is common. Just proceed as normal.
The officer might have wondered if your documents are genuine or a (good) forgery. That can sometimes be gauged by asking a couple of rambling questions and see if the answers are coherent. That starts with “what is your birthdate” even if they have the passport directly in front of their eyes and goes from there.
In that sense yes, he questioned your nationality.
Turned comment into answer per @Gayot Fow suggestion
You can consider yourself extremely lucky, if the was the weirdest question you ever got at immigration. Immigration officers are supposed to ask some off beat questions to gauge your reaction. See http://www.statewatch.org/news/2007/jan/uk-ho-immig-decision-making-study.pdf
Credit:stackoverflow.com‘