It looks like it might be a custom format, which might make sense for the project, but is unfortunate for a broader accessible knowledge-base and programmable integration - plain text allows you "grep", sqlite allows you SQL.
The discussion of this being an org-mode mindset kind of GUI definitely appeals to me. The arbitrary hierarchy of data/knowledge in org-mode works really well for me. I tried a bunch of note-taking apps until org-mode, and it was the second one that just "worked" for me (Trilium Notes and Obsidian were the previous best options for different reasons).
But... I'm an Emacs convert just for the purposes of org-mode, and I'm finding a lot of Emacs specific quirks and issues that I don't really want to spend time fixing - but customizing until the quirks are your own preferred quirks seems to be the entire culture of Emacs.