Sara J. Maas sold A Court of Thorns and roses as New adult.
https://bit.ly/2OacO8Z

Perhaps because Maas started writing online, she doesn’t feel as tied to the traditional format and is more willing to experiment within the genre. For example, she recently sold a fantasy trilogy under the label of New Adult. For those unfamiliar with the category, that’s because it’s new enough that Maas feels unqualified to define it in her own words. She finds this definition interesting, though: “Young Adult is figuring out your place in the world and how you fit into it, and New Adult is once you’ve found your place in the world, what you do next.

Mainstream media and some websites are marketing as Young adult/Children because that's how the publisher needs them marketed, and that misleads people to shelve as Young adult but the author says her books are new adult.

The people who read the book have shelved them those books as New adult because pornographic content and because the characters are adult, not teens.