yeah probably it's not expressed very well. You don't need to learn the syntax of erlang to understand Elixir. You can call any erlang code from within Elixir in a format that almost completely looks like elixir (the difference is that Erlang modules have a colon and start with a lower case and Elixir modules are upper case).
You might need to learn to read erlang documentation. But I've done quite a bit in Elixir, from standing up websites to writing a VM orchestration engine, and the only things I've needed to read the erlang docs for were:
1) writing an Elixir library that wraps the builtin erlang :ssh module with a more elixirish syntax
2) writing an Elixir library that wraps the builtin erlang :gen_statem module with a more elixirish structure and syntax
3) writing an Elixir library that fixes and wraps the builting :tftp module with a more elixirish syntax
4) figuring out how erlang uses SSL so that I could write a two-way encrypted SSL rpc library.
I did them for fun, but all of these are either in prod or used to make production artifacts, and all of these are of course open source and available, so you can use them and not have to do what I did.
Also FWIW, I have read exactly zero of those books.
