Viva voce question about another student "validating" my results
I suspect your supervisor was thinking about how that student confirmed your results. A classic way this could happen is, if you solved a problem with one method and then the other student solved the same problem with a different method, and your results agree, then the other student has "validated" your results. Naturally, you don't need to have worked with each other to do this - in fact it's arguably preferable that you don't work with each other, to ensure independence of results. Neither do you need to be able to cite their work (you can just say "unpublished").

It's always good to have someone validate your results, because it increases the chances that your results are robust and not due to, e.g. statistical noise. If someone has validated your results, it's definitely something to mention.