Young adult fiction being the fing young adults read the most makes 100% sense.
> I think the curriculum generally agrees and assigns what we'd call adult literature in high school English.
The curriculum assigns what they should read to get overview of history of literature and general education. You are not meant to like most of it, you are meant to learn about the writer and period from it. The curriculum does not assigns what they "should" read for pleasure or like.
I am from generation that read a lot. Huge bulk of what people, both adults and teenagers, read was something called "junk literature". It is fascinating how the "kids don't read for pleasure" panic instantly jumps into "it is horrible that when kids read for pleasure, they report liking books that are age appropriate and written so that their generation likes them".
> "junk literature" ... fascinating ... panic
Yes. It's funny how old this meme is. It's about as old as novels, at least. It's fun reading centuries-old novels and finding references (well, thinly veiled protests) to the holier than thou impeccable paragons of virtue that have nothing better to do than hassle someone who wishes to read a book.
I suppose there's been some progress, if the fiction police have had to retreat to a limited subset of fiction to call sinful.
I never said a kid should not be allowed to read books outside of their demographic bracket. Kids can read books "officially" for younger kids, older kids or adults assuming it does not contain genuinely 18+ content. A kid reading book meant for young adults will typically miss some themes, topics or relationships. It will relate characters differently, will miss some motivation and some stuff flies over their head. I personally missed most of the sex in Witcher when I read it the first time when I was too young to figure them out. I thought some characters are just mean when adult me understood exactly why they do what they do.
Young adult category is not meant or written for 9-12 years crowd. That does not mean kids brain will melt. My own kids have seen and enjoyed entertainment meant for older people - but it was super apparent a lot of it went right over their heads when I talked with them.
By contrast, in high school we were assigned books like Brave New World, which makes a lot more sense as a book for that age range and is more what I'd think "young adult" should mean.
It doesn't refer to "actual adults", no: The age range is usually said to be 13..18.
The target audience is largely teenagers who want to read what they want to read.
What's your problem with "kids" reading books, anyway?
I'm firmly in the camp that I am a better person today because things like parental controls did not really exist in the world when I was a kid, and I was playing GTA at like 10. While kids today at that age are forced to read, listen, watch or play dumbed down crap.
Second, why is it shocking that smart educated Ivy League student would enjoy a book written for the young adult category? They read manga, superhero comicd, they watch same series on TV. Are you similarly shocked they watch football and their favorite movie is not from 1959?