There are always going to be niche langauges and mainstream languages, and as a result, users of niche languages will always have to "justify" their use of such. To investors, to potential new users, to potential colleauges.
They're not having a bash at $your_favorite_langauge. Or suggesting that nubank couldn't have been built on any other platform. They are simply responding to the oft-stated question "are there any examples of it working at scale".
What do you care whether it's "the right way" to develop any kind of software? "Clojure" was in the title. If you don't like Clojure, skip along to the next article.