Personally I've seen hundreds of projects in many languages called "blazing fast". To me they're meaningless words.

Elixir and Erlang are bad at number crunching, they aren't "fast" at computations like C is. However, because of the amazing piece of tech that is the BEAM, problems that are best solved through multiple processes/actors, concurrency, and distribution appear to be "blazing" fast because the two languages are very good at that type of stuff. Hence the Phoenix web framework being called "blazing fast"—the BEAM is great for servers.