The staffer was right.
Back in June a staffer who used to periscope a lot let it slip that GMW was not getting renewed. The staffer disappeared from social media after that. People said he was a no one, didn't know anything, etc. So they all new, staff and actors, since at least June the show was being canceled. I'm sure they hoped Disney would change their minds. But unless your blind there have been so many indications. The way the last taped episode was, very emotional, the yearbook, parts of the set being sold, Peyton Meyer saying he needed to look for work this year, rider strong saying the show ended.
Don't doubt the prop master.