I have not visited the High Line yet but it looks a really good place to me and I would love to see it. As to why it is classified as landscape urbanism, I cannot really say. In my view Landscape Urbanism is a design method for landscape architecture: I am writing an eBook which will explain my understanding of it.

Here is some more information about James Corner’s design
http://www.nextroom.at/data/media/med_binary/original/1121022434.pdf
Much emphasis is placed on habitat creation, very properly. Less is said about the social and aesthetic aspect of the design. I am not able to explain these aspects and have commented on the design method rather than the design result. I think it is a McHarg approach and can be called ‘ecological design’. I do not see much evidence of the Tschumi-Koolhaas ideas which extended McHarg’s approach to create what was at first called Landscape Urbanism and is now being called Ecological Urbanism. I have read that Corner is distancing himself from Landscape Urbanism but am not clear why or when he began doing this.
Rats are nocturnal but they also tend to be active at dawn and dusk – and they make reasonably well behaved pets.