That's fine I think. Elixir is their primary language it seems and using Erlang bits from Elixir is pretty easy, which is nice. It's a great benefit to the BEAM VM ecosystem. I think Elixir is the newer language and people enjoy up-voting it more. They could have said something like using BEAM VM and Cowboy maybe...? But I don't think it's a great misrepresentation either way.