If you were to compare it to a painting or to the Grand Canyon or to the Northern Lights or like an act of kindness or a parent's love for their child or something, then I guess fine, not beautiful.
But for an open source project it's very nice!
(Note: none of the marketing materials for the website chose that word, at first glance. It seems to just be a descriptor given by the HN poster.)
I'm the maintainer of Paseo. This is correct, I do not use the word beautiful anywhere.
I personally do think it's beautiful (obviously), but I would not use that word in marketing materials, I'd rather people judge from seeing the screenshots or trying the product.