Some of these I’ve been told are taboos in the opposite way. For example, the one about serving or taking food from the opposite end of the chopsticks, I was told, is polite. But here they say it is taboo. Maybe they meant it’s taboo not to do that?

Yes, it’s weirdly ambiguous. But even that is performative, as you’re still using an unsanitary part - the part that has touched your hand vs the part that has touched your lips.