And I think I had read that Whatsapp used Erlang because Facebook Chat was using Erlang and they thought Facebook knew what they were doing and decided to use the same tech. What a twist
Where did you read that? I believe Whatsapp used erlang because they leveraged ejabberd [0] for XMPP. Wouldn't surprise me if this is why FB originally used Erlang for the chat servers too.
[0] https://en.wikipedia.org/wiki/Ejabberd