>> To turn the chopsticks around when serving food so that the tips of the chopsticks that have touched one’s mouth do not touch the food.
> Ewww. I’d rather be rude than share germs.
I think this means you should use something other than your chopsticks to share food, and not just assume that "the back of my chopsticks are germ-free, I'll use that"
You will quickly learn the first one because if you keep eating the delicious side dishes you will be only left with large amounts of bland rice to eat last.
Keto diet doesn’t exist in Japanese cuisine. If you’re going to a keto friendly place, it’s something trendy and contemporary so this traditional advice obviously doesn’t apply. It is not a faux-pas to eat non traditional / non Japanese cuisine.