Discrepant means "not compatible with the usual" or not in harmony", thus this might mean the behavior is not usual for that person...it's out of the ordinary, or the behavior does not match the words of the person.
One example is a person says one thing, but does another...
Or... their emotions don't match their facial expression...
Or..a person who just smashed their finger with a hammer and breaks it would normally act in pain. Discrepant behavior would be if that person just looked at their smashed and bleeding finger and laughed and acted as if nothing had happened.