Muxer here, and fun fact, Elixir is a core piece of our infrastructure and has been from the start! At the very beginning our dashboard interface was all rendered by Phoenix and occasionally a page would individually include React if it was a situation that truly needed advanced client-side interaction. Given that our first product was an analytics dashboard, that latter situation quickly became basically our entire dashboard and it simply made sense to move to a full SPA taking advantage of the API we were exposing to customers anyway. This was 2016, so LiveView didn't exist at the time, but I'm still not sure I'd make a different decision for that product today.
The blog post is talking about the application that powers our public marketing site, which has a pretty different set of needs, but figured I'd throw it out there that we use and love Elixir/Phoenix! :)