I'd say one talk at an erlang conference three years ago falls into the umbrella of not talking much. The article doesn't say "they never talk about engineering."
And the consensus in our team is that it is largely because of Erlang. We’re managing to serve huge amount of connections from single front-end server (this is from last year’s Erlang
I have found other mentions about it, perhaps on Erlang mail lists, here is an interview with Eugene Fooksman:
https://pdincau.wordpress.com/2013/03/27/an-interview-with-e...
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And the consensus in our team is that it is largely because of Erlang. We’re managing to serve huge amount of connections from single front-end server (this is from last year’s Erlang
"""
I don't know how much clearer can it get.
Here is another directly from their website:
https://blog.whatsapp.com/196/1-million-is-so-2011
It is a bit older they clearly indicate that FreeBSD and Erlang are key and critical elements that let them operate they way they do.