It’s a special type of list called a charlist, a list of integers where all the integers are valid code points. The default inspect behavior is to represent such a list as the more “human readable” charlist. You can use the charlists: false option to inspect it as a list of integers.
This issue comes up every other week or so on elixir forum, don’t worry. Probably the only way it goes away is if in a future version of elixir they get rid of list-encoding Erlang strings with single quotes, but that’s unlikely to happen unless Erlang makes a massive push to deprecate charlist first.