Indeed I am, but the point here is that some users are actually typing em-dashes outside word processors or publishing/typesetting tools (e.g., on HN)—so it's n

Indeed I am, but the point here is that some users are actually typing em-dashes outside word processors or publishing/typesetting tools (e.g., on HN)—so it's not necessarily a sign of a message written by an AI (m-dash pun intended). The poster could as well be a developer with a full-size keyboard.