As a personal bit of development last weekend. I can see inconsistences myself, some of which result from scope creep during development (starting with the idea of a text-only app and then grafting on the web side) - it literally only started because I wanted a working example of bluetooth and dBus in C, the rest of it just joined the ride.
As for the SSE, no expert on that myself, however if you watch the messages in the browser console it appears to push updates with sporadic notes about using polling instead.