The origins of such usage likely can be found in text-based role-playing games in MUDs (Multi-User Dungeons/Domains), which were superseded by IRC and instant-messaging interfaces. As one "Role Play Manual of Style" explains, "Actions are enclosed in asterisks and written in third person perspective." But this type of asterisking has thoroughly infected Usenet posts, blog comments, tweets, and anywhere else online that people feel the need to describe real-world actions in a virtual space.
So, by giving yourself your own stage directions enclosed in asterisks, you treat your own words as lines in a play, and then step outside of your character to give the perspective of the playwright in the play you're acting in. It's all so meta.ᔥ NEILALIEN