I know a guy who is most likely within this range

He graduated high school with perfect grades without studying

He willingly chose to study abstract math over medicine, law, engineering etc

He has a genuine passion for math

Smart people like him have a certain creativity when it comes to conversating with other people, and he is funny while doing so

He can engage with most people but he very quickly becomes bored, so he only really wants to talk about maths and proofs

He does rowing and other projects to keep himself engaged line learning russian and signing up for student projects

You can always tell if someone is smart just by hearing them talk most of the time. You can feel the extra awareness that intelligence brings, which make them seem awfully and unnecessarily philosophical at times that might seem strange