Not everyone who doesn’t have a high GPA is an idiot either. 
Some kids don’t really find HS to their liking or really don’t care about grades too much but find the structure and course choices in college much more appealing.
I think there are lots of assumptions on CC about what majors “smart” kids choose and which majors are for slackers or less intellectual students.
I’d also add that because students can be lopsided in either direction, better in test scores or GPA, but not both, there are likely more kids in that top 25% percent in a given school’s reported GPA/tests scores than 25%.