The following sentence in the section " Erlang, OTP, Elixir, and Friends" is not correct:
“You’ll write Elixir code when you work on your app, but it’s compiled into a totally different programming language called Erlang.”
Elixir is not transpiled to Erlang. In fact, Elixir compiles to BEAM bytecode.
I am sure the author knows and meant to say this, I just wish he had stated it a bit more accurate.