English does this kind of thing all the time, as others have pointed out, but often to understate things somewhat. "Not bad!" actually means pretty good, but the speaker does not want to sound as if gushing. (Maybe it wasn't "fantastic", but still more than acceptable.)

Even the opening example—like if Alice said something truthful but offensive or bombastic, and Bob objects, Carol can say "Well, she's not wrong..."

Back when Americans economically feared the Japanese rather than the Chinese, there was a myth that the Japanese were so conformist that the same word meant both "to differ" and "to be wrong"—chigau (違う). Well, Japanese society is pretty conformist, ngl, but the reality is a bit more subtle. In Japanese it's incredibly rude to tell someone they're wrong so instead they say chigaimasu, "it's different".