The logical conclusion would probably be 'Sam is not hungry' (depending upon the argument). 'Is not' is not equal to 'must not'.Well, as usual, context is everything. I agree that in "Sam must not be hungry," must indicates a logical conclusion (at least usually). However, that's not what it means - at least not to me - in "You must not be right." If my meaning was "The logical conclusion is that it's not possible that you're right," I'd use can't.
'Sam must not be hungry' can be the conclusion of a logical argument, yes. I am asserting that it cannot simply be substituted for '... is not ...' in a conclusion (and vice versa). Logic is a precise discipline and you would have to advance further argument based upon the premises to show the equivalence (very unlikely that this would be possible. This is one reason why 'correct' vocabulary/grammar is important).I agree that is not is not equal to must not. But if you're saying that must not isn't used to indicate a logical conclusion, I have to disagree because in AmE, it sometimes is. That's not what it's always used for - it isn't in "You must not be right." But it is used that way fairly often.