It's funny you mention WhatsApp and Erlang, because the article actually addresses that point:

> You're more dependent on the decisions made by the language implementers than you think ... some odd case that didn't matter at all for the problem domain the language was created for

The language implementers (employee of Ericsson) made design decisions based on telecom constraints, exactly the same constraints faced by WhatsApp and other messaging systems. In the parlance of the article, WA is in Erlang's problem domain, so a strict interpretation of the author's words would have him agreeing with WhatsApp here