Not the author and have no skin in the game. A link back to the original and referring to their MIT license is probably a good idea for the author of this. But the main difference is that it is a theme for a completely different UI kit. Visually similar, but this is for Bootstrap CSS, whereas shadcn is for React. (These are not opposites, but you can use either without the other.)

In fact, that could even be the headline of the website: Want to use shadcn but don't want to rewrite your application in React? Use Shade/Bs!