They're one of the many success stories in the community of startups who have chosen Clojure as their primary weapon. (See also: Climate Corp, now owned by Monsanto.)
Lisp is having its victories, here and there, but notably in meaningful and economically real ways.
Edit: They DO NOT use ClojureScript, sadly. Unlike say, CircleCI or Prismatic, who both have very compelling stories with regard to using Clojure from the front to the backend.