What should I say about a publication that I have not contributed to?
Cut shortly, use it to your advantage, but be honest. If you're in the project, that means you should know the aims, tasks and problems of it. Even if you did not contribute to the article directly, experimental or literature research is still relevant and could be used by your colleagues. Try to figure out to see it clearly and be able to explain.
And of course if you include this publication to your CV, you should know as much as possible about the topic. That could be educational for you as an undergraduate.
Good luck!