How advanced is it if a 1st grader understands the Pythagorean theorem?

Unfortunately, it's not my child.
It's a son of a friend who lives in the same apartment complex and the same building,
and we've been close since before he started elementary school.
This kid...
is in 1st grade...
but he is incredibly good at science and math compared to his peers.
They say he memorized the multiplication tables perfectly before he was 5...
And now that he's in 1st grade...
he's solving things like the Pythagorean theorem, least common multiples, and functions.
Lately, it seems like he can only solve them if he understands the question itself.
The fact that he can understand the wording of the problems is just amazing.
It's not my kid, though. lol