If I understand it correctly, it is decentralized. When pages are accessed they are automatically copied and hosted by nodes. Eventually, garbage collection will delete the copy. Pinning prevents it from being deleted so that the node hosts it permanently.
As far as I'm aware the 'automatic copying and hosting' currently lasts for around 30 minutes. You need to manually pin anything you want to live for longer than a day for sure.
Additionally, this project utilizes IPNS, which clears it's DHT of entries that haven't refreshed within the past 24 hours. So you DEFINITELY need at least one node online, pretty much always, for this content to load.
