The proposal here seems to be that data, as Linked Data (as RDF, specifically) be exposed directly to the web, manipulated by rich front ends written in JS using an RDF parser. The marketing speak is so thick that it’s impossible to discern much of the technical detail, but presumably the server side is an LDP server backed by something (triplestore?).

RDF, LDPs, and Linked Data in general are all child projects of the Semantic Web movement, and nigh-on inseparable from it in practice. The venn diagram of their user communities is one circle.

Maybe this disagreement about what Solid is demonstrates the GP's point that the intro site is a piece of PR puff so that nobody knows what it's supposed to do.