"Who is that?"
So the in-universe audience surrogate was a humanoid figure after all, or a phone camera that's actually connecting to someone via video call. Spoopy as hell, especially if the person on the other end is actually human. That is a very likely possibility considering the theme of the story Yuuma told this time (a ghost inciting people to commit self deletion). Thinking back, Yuuma's stories often have vibes of him trying to express his own feelings or situation albeit in a roundabout way.
I'd be pissed off if it turned out he is doing a livestreaming series, planning to have it up until his actual suicide, to an audience of 2ch trolls