Clarity UI is pure CSS: you just include it on your page, use the correct markup and classes and our styles will be applied. Kind of like using Bootstrap without their JS (most of us have done this).
Clarity NG depends on Clarity UI for styling, but provides full-blown Angular 2 components with the correct markup in their templates, two-way binding, ... That's the easiest way to use Clarity, but it forces you to use Angular.
Unfortunately, our documentation doesn't split the two yet, it starts with the pure HTML/CSS version and then showcases the Angular 2 components after that. Probably explains the confusion.
I hope this helped!
That's where the confusion come from, thanks for explanation!