Do you have a link to that demo?
Rails, it was this one 17 years ago: https://www.youtube.com/watch?v=Gzj723LkRJY
Live View, I'm not sure which is the first demo. There's "Build a real-time Twitter clone in 15 minutes with LiveView and Phoenix 1.5" (https://www.youtube.com/watch?v=MZvmYaFkNJI)