It’s not impossible that a question or comment could seem irrelevant to you. It’s not impossible you could start responding to a question but go off topic from the discussion. However it happens, if you experience any confusion because you need to talk about something unexpected:
Think about what’s being asked or discussed. Then decide how you can best proceed.
In the case of off-topic questions from examiners, you might really believe a question is irrelevant. Totally off-topic, completely unimportant. You could say that…
…but will that help? It might be better to explore the topic and try to respond as well as you can, to begin with. You could still say you don’t think it’s all that important afterwards, but perhaps give it a little time first.