Erlang and Elixir aren't the same language, but they do share a pretty unique architecture in OTP. When people talk about "the advantages of Erlang" they're frequently really talking about OTP (that, or BEAM's reduction-counting ISA.) So people think it's Erlang that gives you those advantages.

Of course, it's not; any language that targets BEAM could pick up those advantages "for free", in the same way Clojure gets a bunch of Java libraries "for free." But people compare programming languages, not abstract machines or library ecosystems. If you treat Erlang and Elixir as black boxes, hiding BEAM and the OTP (the way someone who doesn't know either language would), then they seem to be much more similar to one-another than any other language is to either of them.