I can see both sides.
I don't think I'd be outraged, but I would probably eyeroll. They were clearly doing it for attention, which I don't think is really in the spirit of naturism.
My young kids would probably have laughed, but they would have initially been shocked and they probably would have looked to me to take their lead.
I also think hygienically it's not great in a restaurant.
But the couple have got what they wanted - attention.
So actually, no, I initially said I could see both sides, but no, I think they were being needlessly attention seeking which is not in the spirit of being a naturist.
Overall - a massive eye roll and a slow handclap for them.