Pretty sure he was just live-tweeting during the AMAs since it was on in our timeslot and had nothing to do with her potentially being on the show.
Also there would be riots if anybody other than Mandy Moore took the role of Rapunzel and Zac Levi for Flynn. There’s just no excuse not to have them so I seriously seriously doubt that this was anything other than congratulating someone on winning an award that was on during our regularly scheduled showtime.