My understanding is that this loads content from various protocols (listed at the top of the page), many of which support replicating data in a decentralized way. As far as I know, there's no blockchain involved in anything here yet.
If you browse to the Community Video section and choose a video, you can see peer information as though downloading through WebTorrent. If I disable WebTorrent and look at a video, I don't see the peer information and it seems to fall back to HTTP. Pretty cool! It looks like almost everything is only seeded by the Internet Archive right now, but hopefully they want to encourage more people to participate.