Surely they mean Erlang not Elixir
A note on terminology: Throughout this post I refer to "the BEAM." BEAM is
the virtual machine that runs both Erlang and Elixir code, similar to how the
JVM runs both Java and Kotlin. Erlang (1986) created the VM and the
concurrency model. Elixir (2012) is a modern language built on top of it with
better ergonomics. When I say "BEAM," I mean the runtime and its properties.
When I say "Elixir," I mean the language we write.Elixir just feels… Like it’s a load of pre-compile macros. There’s not even a debugger.
Elixir adds a few things (a lisp-style macro system, protocols, UTF-8 as the default string type, a builtin build tool, streams) but Elixir is not a huge departure from Erlang in the way that Clojure is a huge departure from Java.
By far the biggest things you're going to learn when you learn either one are going to be the BEAM runtime itself and the OTP libraries, which both Elixir and Erlang have in common.