Sounds more like Bootstrap. Bootstrap is what ALL hipster startup websites use. Bootstrap's philosophy is mobile-first. In that they care more about providing the best usability on mobile. Maybe passable usability on desktop.
The W10 "desktop" apps I've used so far all smell like mobile apps and generally feel like a novelty more then anything else. In fact, now that I think about it, they look and feel and generally are designed like Bootstrap-powered web pages. Now I realize that's a symptom of Microsoft adopting the Bootstrap philosophy. Unfortunately, mobile-first only makes sense when your mobile platform is dominant. Maybe that is what Microsoft was hoping for. :)
i don't think he said it was a new idea; he was just explaining how it works.