It means you never know how smart someone is unless they can demonstrate it is like walking your talk. if your say you are smart but never back it up with anything then no one can really know if that person is smart. opposite goes for it too if someone gets good grades speaks intellectually and shows they are intelligent then they are smart because you are able to asses by their behavior and work results
To know if a person has knowledge, you should access how smart that individual is by evaluating the reasoning capacity of that individual in various aspects. Being knowledgeable comes with demonstration of certain attributes which will show your are different from others. For example, if a person has innovative ideas and concepts that can be made into real outcomes, then it is said that he or she is educated/of high IQ. In schools, teachers use exam to know if the students can demonstrate their levels of understanding where the results will categorize them according to their level of understanding. It is common to associate intellectuals with good grades though a smart person can be identified by his or her behavior and works including the manner she or he tackles challenges.
