I would not compare those two situations. When you are pointing out someone has misused a word, that's superficial. The word is wrong, but every one understood

I would not compare those two situations. When you are pointing out someone has misused a word, that's superficial. The word is wrong, but every one understood the actual meaning. I would only do this if I think it may interest the people around and could lead to an interesting discussion, but would remain silent about this otherwise. Unless, of course, there's a real (risk of) misunderstanding (then, people are thankful you lifted the misunderstanding, instead of being annoyed). If you just say "what he actually meant" when everybody got what he actually meant (even you, since you were able to suggest the right word), that probably just feels pedantic indeed. While he is pointing out the difference between being out of tune with itself, or with another instrument, and out of tune in general because he means different things, different actual concepts, and needs the other musicians to understand the difference when using these terms, because their meaning is indeed widely different. He is clarifying what he, himself, means when he says out of tune, trying to fix an actual misunderstanding. tl;dr: in one situation, the actual intended meaning is likely going through correctly even if the words are incorrect. In the other, the meaning is lost because of imprecise understanding of the term. The first one is not really problematic. The second one is critically problematic. Now, of course, he could probably have clarified this thing in a 5 times shorter video (this is no rocket science) without making a mountain out of a molehill, and him pointing out out of tune things to people who don't care would probably feel equally pedantic.