That's a nonsensical point, though. Building a proof of concept in a language and then rebuilding the practical implementation of it in another language and runtime doesn't make the two the same thing. If Notch had built a proof of concept of Minecraft in Python before building the Java version, we wouldn't say Minecraft was originally written in Python. There wasn't even a robust way to compile OCaml for the web in 2010/2011 even if you wanted to try to use the same code. My understanding is that zero SML or Ocaml related to React ever ran in production, which makes the assertion that it was used in anything other than an academic capacity moot.

Hell, Facebook's own XHP's interface (plus PHP/Hack's execution model) is more conceptually relatable to React, and its initial development predates Jordan's time at Facebook. It wasn't JavaScript, but at the very least it defined rails for writing applications that used the DOM.