I am a bit disappointed, they promised a lag free network stack, but they just use websockets, so that's an empty promise. You can't have realtime multiplayer without UDP.
I think we need to update that bit in the whitepaper, it was written long before we developed our WebGL stack which as you pointed out now uses WebSockets. We are working on a multiplayer version of Score Rush that would be available on our website for everyone to try.