The title is a Malay word usually translated as immigrant but the movie chose 'outsider'. Sometimes you can hear the supernatural entities referred to as such too, and it's a function of what verb this word made a noun of, which is "to come". Quite literally it's the one who comes (from somewhere else), and that is the definition the movie played with.

It's definitely polemical, and a story that is more an allegory with the lightly sketched-in characters serving as a placeholder for the audience's own assumptions and baggage. The worldbuilding as well is as light - the movie wants to do Discourse more than actually explore the premise and how the chars would react to it. So in that sense, the movie doesn't have any surprises but I do applaud the fact that a Malaysian dystopian setting is a rare creature as a feature. Worth a watch at least.