To me that's nonsense. If someone has more talent for sports than for studying why take it against them if they invest more time and effort in what they're really good at. I'm a lot more interested what his basketball coach has to say about him.
And what does a counselor know about these kids anyhow? Unless he saw him regularly because of misdemeanour, he probably doesn't have much more on him than the standard conclusions based on his school reports. These people have hundreds of kids under their wing, do they really know them?
a) The counselor is a "she", not a "he".
b) DeMatha is a private catholic school of about 800, which means there would be about 200 in a graduating senior class. A good counselor would have no problem knowing all the seniors pretty closely after 4 years. Especially any that actively seek out their assistance.
c) Fultz was already on scouts radar and shooting up the rankings. You can bet every administration and faculty member knew who he was very well.
d) DeMatha is a national basketball prep powerhouse with a long history of alumni going on to the NBA so they are very tuned in from the day a kid like that arrives with what he needs for a 'basketball career' both in college and the NBA.