Strings in Elixir are, by definition, UTF-8 encoded.
When you inspect a binary (a binary is a bitstring that is divisible by 8 bits - therefore a String is also a binary encoded as UTF-8), Elixir will output it as a string if it is valid UTF-8. It will output it as a binary if it is not.
Therefore basically your data is not valid UTF-8 and is therefore not a String.
You can chunk the binary by the valid String parts as follows:
iex> binary = <<253, 55, 122, 88, 90, 0, 0, 4, 230, 214, 180, 70, 2, 0, 33, 1, 22, 0, 0, 0, 116, 47, 229, 163, 224, 46, 175, 14, 134, 93, 0, 22, 233>>
iex> String.chunk(binary, :valid)
[
<<253>>,
<<55, 122, 88, 90, 0, 0, 4>>,
<<230>>,
<<214, 180, 70, 2, 0, 33, 1, 22, 0, 0, 0, 116, 47>>,
<<229, 163, 224>>,
".",
<<175>>,
<<14>>,
<<134>>,
<<93, 0, 22>>,
<<233>>
]
That suggests your data is encoded in some very different way to UTF-8.
