I think if you don't know if someone will understand you or not, you err on the side of caution and assume that he/she will and avoid saying anything that you wouldn't say in front of someone who would understand you. In fact, I'd say you might as well just make it a rule not to say in front of someone anything you wouldn't mind him/her hearing, regardless of whether he/she speaks the same language as you do or seems fully capable of understanding you. It drives me nuts, for instance, when people assume Alzheimer's patients are incapable of following a conversation, so it's just fine to go on about them right in front of them. It's rude, whether they understand you or not. For all her other faults, in this particular case, I think Jennifer got it right: try to treat other people's sacred spaces with the same respect you'd like afforded yours. She may very well also have beliefs that are closer to the Snowboarders' than the Buddhists, but she understood that it was not perhaps the right time to voice them, as she was a guest in their place and their country.
And no, no one ever died of a comment--except that ill-advised comments/arguments about religion and other sensitive topics have caused all kinds of conflicts that have caused all kinds of problems, including the deaths of many people. Words, not just actions, matter--just look at the problems cyberbullying has caused-- and IMO, the snowboarders chose their words poorly and spoke them at the wrong time in the wrong place. Just because you have an opinion doesn't mean you have to immediately voice it, even if you're asked directly about it, and they do bear some responsibility for their choice of words, because the show wouldn't have anything to edit if they hadn't said what they said in the first place.
And I'm sorry I assumed the comments made by the imaginary Muslims or Jews in a barbecue restaurant about their inability to eat the food would necessarily be complaints. Aside from the fact that it's unlikely that Muslims or Jews would ever choose a pork barbecue restaurant as a place to eat, I assumed they wouldn't be commenting pleasantly on the fact that they couldn't eat the food there, because that seemed even more unlikely--but it was only my assumption about your hypothetical example.