It is open source, though the section in the FAQ just links to github.com, but I found the actual source code: https://github.com/patchwork-hub/channels. Seems to be a Mastodon fork, which becomes even more apparent when you actually look at a channel: https://channel.org/@feelgoodart

From what I can gather, this is a way of having an account boost content from certain creators or hashtags with some filters applied on top, honestly pretty cool but I wish they explained it better than 'connecting the open social web'. Like the page explaining it has a terminal case of marketing speak.