My soup

When taken literally, the phrase, "Yeah, right" actually means something along the lines of, "Yes that is correct." To a foreign learner of the English language this would be read as a double positive resulting in a positive, unless they understood the concept of sarcasm. The implication of sarcasm that this situation presents leads an English speaker to understand that in this context the student's response of, "Yeah, right" is two positives equating to a negative. Point being, the student's response may be taken as either a positive or a negative, although literally speaking it still is not a negative double positive.