My view was that that scene is entirely Arthur's delusion. The delusion of social acceptance, transmuted to the delusion of being in a place of judgement. Arthur wants to see himself as the kind of person sending the message you're discussing.
I think it totally played out like we see. When his meds start to wear off and he wakes himself up from his girlfriend delusion, when he stops feeling like he doesn't exist and starts to accept that he's the way he is and enjoying it, I think the delusions are over. He doesn't need the escapism of inventing a life in his head, for the first time he feels he is who he wants to be.
"Like the old proverb says, if one sees something not right, one must draw out his sword to intervene"