Thanks for clarifying. It's not obvious enough on the site. Most WP users will be looking for something obvious whilst scanning. It should probably say this on the homepage. I assumed they modified core at first look.

You could be forgiven for thinking that, since the first claim on the home page is

> Layers is built into the WordPress core, creating a familiar but joyful building experience.

"Built into the WordPress core" is a very different thing from "is a theme framework."