Without knowing your dynamic or their tone:
They probably just wanted to poke fun and baited you into setting it up. It’s kinda like updog or ligma.

Of course, it could also be ignorance, or malice, but personally, I don’t randomly ask people what OS they use unless I expect them to even understand that question. Their reply suggests they are well aware that you’re using Linux, so ignorance is unlikely, and if they knew your answer and didn’t want to hear it, they probably wouldn’t ask.