I think that in Anglo-American culture it's also usually a faux-pas to confront a 'phony' in casual conversation. I've met lots of phonies in my time, and I feel as though calling them out on their BS stories, even in a subtle way, would have been a bigger faux-pas than telling it in the first place. It makes sense, I guess. Forcing the person to lose face and admit their lie would sour any social occasion.